Title: p27kip1: A Multifunctional Cyclin-Dependent Kinase Inhibitor with Prognostic Significance in Human Cancers
Abstract: p27kip1 (p27) is a member of the universal cyclin-dependent kinase inhibitor (CDKI) family. p27 expression is regulated by cell contact inhibition and by specific growth factors, such as transforming growth factor (TGF)-β. Since the cloning of the p27 gene in 1994, a host of other functions have been associated with this cell cycle protein. In addition to its role as a CDKI, p27 is a putative tumor suppressor gene, regulator of drug resistance in solid tumors, and promoter of apoptosis; acts as a safeguard against inflammatory injury; and has a role in cell differentiation. The level of p27 protein expression decreases during tumor development and progression in some epithelial, lymphoid, and endocrine tissues. This decrease occurs mainly at the post-translational level with protein degradation by the ubiquitin-proteasome pathway. A large number of studies have characterized p27 as an independent prognostic factor in various human cancers, including breast, colon, and prostate adenocarcinomas. Here we review the role of p27 in the regulation of the cell cycle and other cell functions and as a diagnostic and prognostic marker in human neoplasms. We also review studies indicating the increasingly important roles of p27, other CDKIs, and cyclins in endocrine cell hyperplasia and tumor development. p27kip1 (p27) is a member of the universal cyclin-dependent kinase inhibitor (CDKI) family. p27 expression is regulated by cell contact inhibition and by specific growth factors, such as transforming growth factor (TGF)-β. Since the cloning of the p27 gene in 1994, a host of other functions have been associated with this cell cycle protein. In addition to its role as a CDKI, p27 is a putative tumor suppressor gene, regulator of drug resistance in solid tumors, and promoter of apoptosis; acts as a safeguard against inflammatory injury; and has a role in cell differentiation. The level of p27 protein expression decreases during tumor development and progression in some epithelial, lymphoid, and endocrine tissues. This decrease occurs mainly at the post-translational level with protein degradation by the ubiquitin-proteasome pathway. A large number of studies have characterized p27 as an independent prognostic factor in various human cancers, including breast, colon, and prostate adenocarcinomas. Here we review the role of p27 in the regulation of the cell cycle and other cell functions and as a diagnostic and prognostic marker in human neoplasms. We also review studies indicating the increasingly important roles of p27, other CDKIs, and cyclins in endocrine cell hyperplasia and tumor development. Recent studies have shown that cyclins and cyclin-dependent kinase (CDK) complexes have important regulatory roles during cell cycle progression1Sherr CJ G1 phase progression: cycling on cue.Cell. 1994; 79: 551-555Abstract Full Text PDF PubMed Scopus (2642) Google Scholar, 2Hunter T Pines J Cyclins and cancer. II. Cyclin D and CDK inhibitors come of age.Cell. 1994; 79: 573-582Abstract Full Text PDF PubMed Scopus (2202) Google Scholar, 3Sherr CJ Roberts JM Inhibitors of mammalian G1 cyclin-dependent kinases.Genes Dev. 1995; 9: 1149-1163Crossref PubMed Scopus (3227) Google Scholar, 4Kamb A Cell-cycle regulators and cancer.Trends Genet. 1995; 11: 136-140Abstract Full Text PDF PubMed Scopus (298) Google Scholar, 5Massague J Polyak K Mammalian antiproliferative signals and their targets.Curr Opin Genet Dev. 1995; 5: 91-96Crossref PubMed Scopus (113) Google Scholar, 6Clurman BE Roberts JM Cell cycle and cancer.J Natl Cancer Inst. 1995; 87: 1499-1501Crossref PubMed Scopus (94) Google Scholar, 7Sherr CJ Cancer cell cycles.Science. 1996; 274: 1672-1677Crossref PubMed Scopus (5032) Google Scholar (Figure 1). Cyclin-CDK complexes are in turn regulated by the cyclin-dependent kinase inhibitors (CDKIs), which generally inhibit cell cycle progression (Table 1). These proteins fall into two families based on their structural and functional properties. The INK4 group includes p16/INK4A (p16), p15/INK4B (p15), p18/INK4C (p18), and p19/INK4D (p19). They all have four ankyrin repeats and form complexes with CDK4 and/or CDK6 and the D-type cyclins. They have functional activities that are dependent on the presence of a normal retinoblastoma protein.8Guan KL Jenkins CW Li Y Nichols MA Wu X O'Keefe CL Matera AG Xiong Y Growth suppression by p18, a p16INK4/MTS1- and p14 INK4B/MTS2-related CDK6 inhibitor, correlates with wild-type pRb function.Genes Dev. 1994; 8: 2939-2952Crossref PubMed Scopus (753) Google Scholar, 9Hirai H Roussel MF Kato JY Ashmun RA Sherr CJ Novel INK4 proteins, p19 and p18, are specific inhibitors of the cyclin D-dependent kinases CDK4 and CDK6.Mol Cell Biol. 1995; 15: 2672-2681Crossref PubMed Scopus (590) Google Scholar, 10Chan FK Zhang J Cheng L Shapiro DN Winoto A Identification of human and mouse p19, a novel CDK4 and CDK6 inhibitor with homology to p16ink4.Mol Cell Biol. 1995; 15: 2682-2688Crossref PubMed Scopus (338) Google Scholar Maximal expression of the INK4 proteins occurs during the middle of the S phase in proliferating cells. Both p15 and p16 show a high frequency of gene deletions, and various human tumors and cell lines have mutations of the p16 gene, suggesting that these genes may function as tumor suppressors.11Hirama T Koeffler HP Role of the cyclin-dependent kinase inhibitors in the development of cancer.Blood. 1995; 86: 841-854Crossref PubMed Google Scholar, 12Jin X Nguyen D Zhang WW Kyritsis AP Roth JA Cell cycle arrest and inhibition of tumor cell proliferation by the p16/INK4 gene mediated by an adenovirus vector.Cancer Res. 1995; 55: 3250-3253PubMed Google Scholar, 13Reed JA Loganzo Jr, F Shea CR Walker GJ Flores JF Glendening JM Bogdany JK Shiel MJ Haluska FG Fountain JW Loss of expression of the p16/cyclin-dependent kinase inhibitor 2 tumor suppressor gene in melanocytic lesions correlates with invasive stage of tumor progression.Cancer Res. 1995; 55: 2713-2718PubMed Google ScholarTable 1Members of the Cyclin-Dependent Kinase Inhibitors of the INK4 and Cip/Kip FamiliesFamilyChromosome LocationINK4 p15 (INK4B)9 p21 p16 (INK4A)9 p21 p18 (INK4C)1 p32 p19 (INK4D)19 p13Cip/Kip p21 Waf1/Cip16 p21 p27 Kip112 p13 p57 Kip211 p15 Open table in a new tab The second group of CDK inhibitors, the Cip/Kip family, includes p21/WAF1/CIP1 (p21), p27/kip1 (p27) and p57/kip2 (p57).14Polyak K Lee MH Erdjument-Bromage H Koff A Roberts JM Tempst P Massague J Cloning of p27kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals.Cell. 1994; 78: 59-66Abstract Full Text PDF PubMed Scopus (2112) Google Scholar, 15Xiong Y Hannon GJ Zhang H Casso D Kobayashi R Beach D p21 is a universal inhibitor of cyclin kinases.Nature. 1993; 366: 701-704Crossref PubMed Scopus (3291) Google Scholar, 16Toyoshima H Hunter T p27, a novel inhibitor of G1 cyclin-cdk protein kinase activity, is related to p21.Cell. 1994; 78: 67-74Abstract Full Text PDF PubMed Scopus (1982) Google Scholar, 17El-Deiry WS Tokino T Velculescu VE Levy DB Parsons R Trent JM Lin D Mercer WE Kinzler KW Vogelstein B WAF1, a potential mediator of p53 tumor suppression.Cell. 1993; 75: 817-825Abstract Full Text PDF PubMed Scopus (8165) Google Scholar, 18Polyak K Kato JY Solomon MJ Sherr CJ Massague J Roberts JM Koff A p27 kip1, a cyclin-Cdk inhibitor links transforming growth factor-β and contact inhibition to cell cycle arrest.Genes Dev. 1994; 8: 9-22Crossref PubMed Scopus (1893) Google Scholar, 19Matsuoka S Edwards MC Bai C Parker S Zhang P Baldini A Harper JW Elledge SJ p57/Kip2, a structurally distinct member of the p21/CIP1 Cdk inhibitor family, is a candidate tumor suppressor gene.Genes Dev. 1995; 9: 650-662Crossref PubMed Scopus (918) Google Scholar, 20Lee MH Reynisdottir L Massague J Cloning of p57 Kip2, a cyclin-dependent kinase inhibitor with unique domain structure and tissue distribution.Genes Dev. 1995; 9: 639-649Crossref PubMed Scopus (858) Google Scholar, 21Ponce-Castaneda MV Lee M-H Latres E Polyak K Lacombe L Montgomery K Mathew S Krauter K Sheinfeld J Massague J Cordon-Cardo C p27kip1 chromosomal mapping to 12p 12–12p 13.1 and absence of mutations in human tumors.Cancer Res. 1995; 55: 1211-1214PubMed Google Scholar, 22Kato JY Matsuoka M Polyak K Massagué J Sherr CJ Cyclic AMP-induced G1 phase arrest mediated by an inhibitor (p27kip1) of cyclin-dependent kinase 4 activation.Cell. 1994; 79: 487-496Abstract Full Text PDF PubMed Scopus (726) Google Scholar These proteins inhibit kinase activities of pre-activated G1 cyclin E-CDK2, cyclin D-CDK4/6, and other cyclins. The Cip/Kip proteins are designated as universal CDKIs because they interact with various CDK complexes, with cyclins A, E, D1, D2, and D3, and CDKs.15Xiong Y Hannon GJ Zhang H Casso D Kobayashi R Beach D p21 is a universal inhibitor of cyclin kinases.Nature. 1993; 366: 701-704Crossref PubMed Scopus (3291) Google Scholar Overexpression of the kip proteins leads to cell cycle arrest. Members of the kip proteins share a great deal of homology. p27 protein has a 42% amino acid homology with p21 and a 47% homology with p57 at the amino-terminal domain, the region that mediates inhibition of CDK. Kip proteins all have a nuclear localization signal at their carboxyl-terminal domain. Unlike the INK4 group, which inhibits CDK4/6 only, the Cip/Kip inhibitors can also target CDK2 in complexes The p27 gene is located on chromosome 12p13 at the junction of 12p12–12p13.1.21Ponce-Castaneda MV Lee M-H Latres E Polyak K Lacombe L Montgomery K Mathew S Krauter K Sheinfeld J Massague J Cordon-Cardo C p27kip1 chromosomal mapping to 12p 12–12p 13.1 and absence of mutations in human tumors.Cancer Res. 1995; 55: 1211-1214PubMed Google Scholar This gene was cloned by several groups in 1994.14Polyak K Lee MH Erdjument-Bromage H Koff A Roberts JM Tempst P Massague J Cloning of p27kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals.Cell. 1994; 78: 59-66Abstract Full Text PDF PubMed Scopus (2112) Google Scholar, 16Toyoshima H Hunter T p27, a novel inhibitor of G1 cyclin-cdk protein kinase activity, is related to p21.Cell. 1994; 78: 67-74Abstract Full Text PDF PubMed Scopus (1982) Google Scholar, 23Slingerland J Hengst L Pan C Alexander D Stampfer M Reed S A novel inhibitor of cyclin-Cdk activity detected in TGF-β-arrested epithelial cells.Mol Cell Biol. 1994; 14: 3683-3694Crossref PubMed Google Scholar Structural analysis of the p27 protein was recently reported.24Russo AA Jeffrey PD Patten AK Massague J Pavletich NP Crystal structures of the p27kip1 cyclin dependent-kinase inhibitor bound to the cyclin A-cdk 2 complex.Nature. 1996; 382: 325-331Crossref PubMed Scopus (805) Google Scholar Examination of the crystal structure of the 69-amino-acid amino-terminal inhibitory domain of p27 bound to the phosphorylated cyclin A-CDK2 showed that p27 binding causes large conformational changes in and around the catalytic cleft of CDK224Russo AA Jeffrey PD Patten AK Massague J Pavletich NP Crystal structures of the p27kip1 cyclin dependent-kinase inhibitor bound to the cyclin A-cdk 2 complex.Nature. 1996; 382: 325-331Crossref PubMed Scopus (805) Google Scholar and that p27 has separate binding sites on the cyclin and CDK subunits. This explains how p27 and other Kip/Cip inhibitors can bind isolated subunits.15Xiong Y Hannon GJ Zhang H Casso D Kobayashi R Beach D p21 is a universal inhibitor of cyclin kinases.Nature. 1993; 366: 701-704Crossref PubMed Scopus (3291) Google Scholar, 24Russo AA Jeffrey PD Patten AK Massague J Pavletich NP Crystal structures of the p27kip1 cyclin dependent-kinase inhibitor bound to the cyclin A-cdk 2 complex.Nature. 1996; 382: 325-331Crossref PubMed Scopus (805) Google Scholar Binding of the p27 cyclin-CDK complex is significantly tighter than binding to the isolated CDK and cyclin subunits, which is consistent with cooperative binding of the two subunits. p27 was first identified in cells treated with transforming growth factor (TGF)-β or by stimulation of contact inhibition where p27 was found as an inactive form bound to CDK2-cyclin E.18Polyak K Kato JY Solomon MJ Sherr CJ Massague J Roberts JM Koff A p27 kip1, a cyclin-Cdk inhibitor links transforming growth factor-β and contact inhibition to cell cycle arrest.Genes Dev. 1994; 8: 9-22Crossref PubMed Scopus (1893) Google Scholar, 25Koff A Ohtsuki ME Polyak K Roberts J Massagué J Negative regulation of G1 in mammalian cells: inhibition of cyclin E-dependent kinase by TGF β.Science. 1993; 257: 1689-1694Crossref Scopus (986) Google Scholar The protein was purified from a cyclin E-CDK2 affinity column and characterized by its strong inhibitory activity toward cyclin E-CDK2. p27 can directly inhibit the enzymatic activity of CDK-cyclin complexes and arrest cells in G1.18Polyak K Kato JY Solomon MJ Sherr CJ Massague J Roberts JM Koff A p27 kip1, a cyclin-Cdk inhibitor links transforming growth factor-β and contact inhibition to cell cycle arrest.Genes Dev. 1994; 8: 9-22Crossref PubMed Scopus (1893) Google Scholar The association of p27 with CDK-4 cyclin D or with CDK2-cyclin E complexes blocks phosphorylation of CDK4 on Thr 172 and CDK2 on Thr 160 via a CDK activation kinase.22Kato JY Matsuoka M Polyak K Massagué J Sherr CJ Cyclic AMP-induced G1 phase arrest mediated by an inhibitor (p27kip1) of cyclin-dependent kinase 4 activation.Cell. 1994; 79: 487-496Abstract Full Text PDF PubMed Scopus (726) Google Scholar, 26Firpo EJ Koff A Solomon MJ Roberts JM Inactivation of a Cdk2 inhibitor during interleukin-2 induced proliferation of human T lymphocytes.Mol Cell Biol. 1994; 14: 4889-4901Crossref PubMed Scopus (281) Google Scholar p27 can be induced by cyclic AMP and other negative regulators of the cell cycle22Kato JY Matsuoka M Polyak K Massagué J Sherr CJ Cyclic AMP-induced G1 phase arrest mediated by an inhibitor (p27kip1) of cyclin-dependent kinase 4 activation.Cell. 1994; 79: 487-496Abstract Full Text PDF PubMed Scopus (726) Google Scholar and can be down-regulated by interleukin 2.26Firpo EJ Koff A Solomon MJ Roberts JM Inactivation of a Cdk2 inhibitor during interleukin-2 induced proliferation of human T lymphocytes.Mol Cell Biol. 1994; 14: 4889-4901Crossref PubMed Scopus (281) Google Scholar The levels of p27 protein are increased in quiescent cells and rapidly decrease after stimulation with mitogens. Constitutive expression of p27 in cultured cells causes cell cycle arrest in the G1 phase.15Xiong Y Hannon GJ Zhang H Casso D Kobayashi R Beach D p21 is a universal inhibitor of cyclin kinases.Nature. 1993; 366: 701-704Crossref PubMed Scopus (3291) Google Scholar, 16Toyoshima H Hunter T p27, a novel inhibitor of G1 cyclin-cdk protein kinase activity, is related to p21.Cell. 1994; 78: 67-74Abstract Full Text PDF PubMed Scopus (1982) Google Scholar When murine BALB/c-3T3 fibroblasts are deprived of serum mitogens, p27 accumulates in these cells.27Coats S Flanagen M Nourse J Roberts JM Requirement of p27kip1 for restriction point control of the fibroblast cell cycle.Science. 1996; 272: 877-880Crossref PubMed Scopus (655) Google Scholar This finding was correlated with inactivation of G1-cyclin-CDK complexes and with cell cycle arrest in G1. Inhibition of p27 expression with antisense oligonucleotides prevents cell cycle arrest in response to mitogen depletion, indicating that p27 is an essential component of the pathway that connects mitogenic signals to the cell cycle.27Coats S Flanagen M Nourse J Roberts JM Requirement of p27kip1 for restriction point control of the fibroblast cell cycle.Science. 1996; 272: 877-880Crossref PubMed Scopus (655) Google Scholar Although p27 inhibits cyclin E-CDK2, recent studies have also shown that p27 can serve as a substrate for cyclin E-CDK2.27Coats S Flanagen M Nourse J Roberts JM Requirement of p27kip1 for restriction point control of the fibroblast cell cycle.Science. 1996; 272: 877-880Crossref PubMed Scopus (655) Google Scholar Using a murine fibroblast model, it was shown that cyclin E-CDK2 can directly phosphorylate p27 (Figure 2), and the cyclin E-CDK2-dependent phosphorylation of p27 results in elimination of p27 from the cell, allowing transition from G1 to S phase.28Sheaff RJ Groudine M Gordon M Roberts JM Clurman BE Cyclin E-CDK2 is a regulator of p27kip1.Genes Dev. 1997; 11: 1464-1478Crossref PubMed Scopus (802) Google Scholar Other investigators demonstrated Ras-mediated down-regulation of p27 that involves suppression of synthesis leading to an increase in the degradation of the p27 protein.29Takuwa N Takuwa Y Ras activity late in G1 phase required for p27kip1 down regulation, passage through the restriction point and entry into S phase in growth factor-stimulated NIH 3T3 fibroblasts.Mol Cell Biol. 1997; 17: 5348-5358Crossref PubMed Google Scholar It is postulated that Ras function is required in late G1 for down-regulation of p27 and passage of the cell through the restriction point.29Takuwa N Takuwa Y Ras activity late in G1 phase required for p27kip1 down regulation, passage through the restriction point and entry into S phase in growth factor-stimulated NIH 3T3 fibroblasts.Mol Cell Biol. 1997; 17: 5348-5358Crossref PubMed Google Scholar The role of TGF-β in regulating p27 has been investigated in many systems.18Polyak K Kato JY Solomon MJ Sherr CJ Massague J Roberts JM Koff A p27 kip1, a cyclin-Cdk inhibitor links transforming growth factor-β and contact inhibition to cell cycle arrest.Genes Dev. 1994; 8: 9-22Crossref PubMed Scopus (1893) Google Scholar, 30Ravitz MJ Yan S Herr KD Wenner CE Transforming growth factor β-induced activation of cyclin E-CDK2 kinase and down-regulation of p27kip1 in C3H 10 T1/2 mouse fibroblasts.Cancer Res. 1995; 55: 1413-1416PubMed Google Scholar, 31Mal A Poon RY Howe PH Toyoshima H Hunter T Harter ML Inactivation of p27kip1 by the viral E1A oncoprotein in TGF-β treated cells.Nature. 1996; 380: 262-265Crossref PubMed Scopus (141) Google Scholar, 32Qian X Jin L Grande JP Lloyd RV Transforming growth factor-β and p27 expression in pituitary cells.Endocrinology. 1996; 137: 3051-3060Crossref PubMed Scopus (100) Google Scholar Using a C3H 10T1/2 mouse fibroblast model it was shown that cyclin E-CDK2 inhibits p27 in the growth-arrested state and that TGF-β down-regulates the steady-state level of the p27 protein.30Ravitz MJ Yan S Herr KD Wenner CE Transforming growth factor β-induced activation of cyclin E-CDK2 kinase and down-regulation of p27kip1 in C3H 10 T1/2 mouse fibroblasts.Cancer Res. 1995; 55: 1413-1416PubMed Google Scholar Mal et al31Mal A Poon RY Howe PH Toyoshima H Hunter T Harter ML Inactivation of p27kip1 by the viral E1A oncoprotein in TGF-β treated cells.Nature. 1996; 380: 262-265Crossref PubMed Scopus (141) Google Scholar showed that mink lung epithelial cells arrested in G1 by TGF-β could be rescued from this arrest by disabling of p27 via adenovirus oncoprotein E1A. Qian et al demonstrated that TGF-β down-regulates p27 protein and mRNA levels in cultured rat anterior pituitary cells.32Qian X Jin L Grande JP Lloyd RV Transforming growth factor-β and p27 expression in pituitary cells.Endocrinology. 1996; 137: 3051-3060Crossref PubMed Scopus (100) Google Scholar There are many putative functions attributed to p27 (Table 2). Extensive investigations have been performed to elucidate the role of p27 as a CDKI in normal and neoplastic cells.14Polyak K Lee MH Erdjument-Bromage H Koff A Roberts JM Tempst P Massague J Cloning of p27kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals.Cell. 1994; 78: 59-66Abstract Full Text PDF PubMed Scopus (2112) Google Scholar, 16Toyoshima H Hunter T p27, a novel inhibitor of G1 cyclin-cdk protein kinase activity, is related to p21.Cell. 1994; 78: 67-74Abstract Full Text PDF PubMed Scopus (1982) Google Scholar, 18Polyak K Kato JY Solomon MJ Sherr CJ Massague J Roberts JM Koff A p27 kip1, a cyclin-Cdk inhibitor links transforming growth factor-β and contact inhibition to cell cycle arrest.Genes Dev. 1994; 8: 9-22Crossref PubMed Scopus (1893) Google Scholar, 27Coats S Flanagen M Nourse J Roberts JM Requirement of p27kip1 for restriction point control of the fibroblast cell cycle.Science. 1996; 272: 877-880Crossref PubMed Scopus (655) Google Scholar, 28Sheaff RJ Groudine M Gordon M Roberts JM Clurman BE Cyclin E-CDK2 is a regulator of p27kip1.Genes Dev. 1997; 11: 1464-1478Crossref PubMed Scopus (802) Google Scholar, 29Takuwa N Takuwa Y Ras activity late in G1 phase required for p27kip1 down regulation, passage through the restriction point and entry into S phase in growth factor-stimulated NIH 3T3 fibroblasts.Mol Cell Biol. 1997; 17: 5348-5358Crossref PubMed Google Scholar, 30Ravitz MJ Yan S Herr KD Wenner CE Transforming growth factor β-induced activation of cyclin E-CDK2 kinase and down-regulation of p27kip1 in C3H 10 T1/2 mouse fibroblasts.Cancer Res. 1995; 55: 1413-1416PubMed Google Scholar Some studies suggest a putative role as a tumor suppressor gene. Loss of p27 protein expression may result in tumor development and/or progression; however, this loss of expression does not appear to result from gene mutations.33Morosetti R Kawamata N Gombart AF Miller CW Hatta Y Hirama T Said JW Tomonaga M Koeffler HP Alterations of the p27/kip1 gene in non-Hodgkin's lymphomas and adult T-cell leukemia/lymphoma.Blood. 1995; 86: 1924-1930Crossref PubMed Google Scholar, 34Spirin KS Simpson JF Takeuchi S Kawamata N Miller CW Koeffler HP p27/kip1 mutation found in breast cancer.Cancer Res. 1996; 56: 2400-2404PubMed Google Scholar, 35St Croix B Florenes VA Rak JW Flanagan M Bhattacharya N Slingerland JM Kerbel RS Impact of the cyclin-dependent kinase inhibitor p27kip1 on resistance of tumor cells to anti-cancer agents.Nature Med. 1996; 2: 1204-1210Crossref PubMed Scopus (303) Google Scholar, 36Tanaka C Yoshimoto K Yang P Kimura T Yamada S Moritani M Saro T Itakura M Infrequent mutations of p27kip1 gene and trisomy 12 in a subset of human pituitary adenomas.J Clin Endocrinol Metab. 1997; 82: 3141-3147Crossref PubMed Scopus (63) Google Scholar More than 500 tumors have been examined for p27 mutations, and less than 5 of these have shown specific mutations.34Spirin KS Simpson JF Takeuchi S Kawamata N Miller CW Koeffler HP p27/kip1 mutation found in breast cancer.Cancer Res. 1996; 56: 2400-2404PubMed Google Scholar These have included a stop codon at position 76 of an adult T-cell leukemia and hemizygous deletion of the p27 gene in a B-cell non-Hodgkin's lymphoma33Morosetti R Kawamata N Gombart AF Miller CW Hatta Y Hirama T Said JW Tomonaga M Koeffler HP Alterations of the p27/kip1 gene in non-Hodgkin's lymphomas and adult T-cell leukemia/lymphoma.Blood. 1995; 86: 1924-1930Crossref PubMed Google Scholar in addition to 2 point mutations in an analysis of 36 primary breast carcinomas.34Spirin KS Simpson JF Takeuchi S Kawamata N Miller CW Koeffler HP p27/kip1 mutation found in breast cancer.Cancer Res. 1996; 56: 2400-2404PubMed Google Scholar One of the mutations in the breast carcinomas was a polymorphous mutation at codon 142 and the other a nonsense mutation at codon 104.34Spirin KS Simpson JF Takeuchi S Kawamata N Miller CW Koeffler HP p27/kip1 mutation found in breast cancer.Cancer Res. 1996; 56: 2400-2404PubMed Google ScholarTable 2Putative Functions of p27Kip1“Universal” cyclin-dependent kinase inhibitor that regulates progression through the cell cycle.1Sherr CJ G1 phase progression: cycling on cue.Cell. 1994; 79: 551-555Abstract Full Text PDF PubMed Scopus (2642) Google Scholar, 2Hunter T Pines J Cyclins and cancer. II. Cyclin D and CDK inhibitors come of age.Cell. 1994; 79: 573-582Abstract Full Text PDF PubMed Scopus (2202) Google Scholar, 3Sherr CJ Roberts JM Inhibitors of mammalian G1 cyclin-dependent kinases.Genes Dev. 1995; 9: 1149-1163Crossref PubMed Scopus (3227) Google Scholar, 4Kamb A Cell-cycle regulators and cancer.Trends Genet. 1995; 11: 136-140Abstract Full Text PDF PubMed Scopus (298) Google Scholar, 5Massague J Polyak K Mammalian antiproliferative signals and their targets.Curr Opin Genet Dev. 1995; 5: 91-96Crossref PubMed Scopus (113) Google Scholar, 6Clurman BE Roberts JM Cell cycle and cancer.J Natl Cancer Inst. 1995; 87: 1499-1501Crossref PubMed Scopus (94) Google Scholar, 7Sherr CJ Cancer cell cycles.Science. 1996; 274: 1672-1677Crossref PubMed Scopus (5032) Google Scholar, 14Polyak K Lee MH Erdjument-Bromage H Koff A Roberts JM Tempst P Massague J Cloning of p27kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals.Cell. 1994; 78: 59-66Abstract Full Text PDF PubMed Scopus (2112) Google Scholar, 16Toyoshima H Hunter T p27, a novel inhibitor of G1 cyclin-cdk protein kinase activity, is related to p21.Cell. 1994; 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85: 733-744Abstract Full Text Full Text PDF PubMed Scopus (1349) Google Scholar, 47Chen J Willingham T Shuford M Nisen PD Tumor suppression and inhibition of aneuploid cell accumulation in human brain tumor cells by ectopic overexpression of the cyclin-dependent kinase inhibitor p27kip1.J Clin Invest. 1996; 97: 1983-1988Crossref PubMed Scopus (82) Google ScholarPromoter of apoptosis.37Katayose Y Kim M Rakkar ANS Li Z Cowan KH Seth P Promoting apoptosis: a novel activity associated with the cyclin-dependent kinase inhibitor p27.Cancer Res. 1997; 57: 5441-5445PubMed Google Scholar, 38Levkau B Koyama H Raines EW Clurman BE Herren B Orth K Roberts JM Ross R Cleavage of p21cipl/wafl and p27kipl mediates apoptosis in endothelial cells through activation of Cdk2: role of a caspace cascade.Mol Cell. 1998; 1: 553-563Abstract Full Text Full Text PDF PubMed Scopus (416) Google ScholarRegulator of drug resistance in solid tumors.35St Croix B Florenes VA Rak JW Flanagan M Bhattacharya N Slingerland JM Kerbel RS Impact of the cyclin-dependent kinase inhibitor p27kip1 on resistance of tumor cells to anti-cancer agents.Nature Med. 1996; 2: 1204-1210Crossref PubMed Scopus (303) Google ScholarRole in cell differentiation in muscle, oligodendrocytes, osteoblasts, and granulosa cells.39Zabludoff SD Csete M Wagner R Yu X Wold BJ p27kip1 is expressed transiently in developing myotomes and enhances myogenesis.Cell Growth Differ. 1998; 9: 1-11PubMed Google Scholar, 40Durand B Gao FB Raff M Accumulation of the cyclin-dependent kinase inhibitor p27/kip1 and the timing of oligodendrocyte differentiation.EMBO J. 1997; 16: 306-317Crossref PubMed Scopus (303) Google Scholar, 41Onishi T Hruska K Expression of p27kip1 in osteoblast-like cells during differentiation with parathyroid hormone.Endocrinology. 1997; 138: 1995-2004Crossref PubMed Scopus (59) Google Scholar, 42Robker RL Richards JS Hormone-induced proliferation and differentiation of granulosa cells: a coordinated balance of the cell cycle regulators cyclin-D2 and p27kip1.Mol Endocrinol. 1998; 12: 924-940Crossref PubMed Scopus (0) Google ScholarSafeguard against inflammatory injury.43Ophascharoensuk V Fero ML Hughes J Roberts JM Shankland SJ The cyclin-dependent kinase inhibitor p27kip1 safeguards against inflammatory injury.Nature Med. 1998; 4: 575-580Crossref PubMed Scopus (181) Google Scholar Open table in a new tab St. Croix et al35St Croix B Florenes VA Rak JW Flanagan M Bhattacharya N Slingerland JM Kerbel RS Impact of the cyclin-dependent kinase inhibitor p27kip1 on resistance of tumor cells to anti-cancer agents.Nature Med. 1996; 2: 1204-1210Crossref PubMed Scopus (303) Google Scholar reported that p27 has a role in regulating drug resistance in solid tumors. Human and mouse tumor cells grown as multicellular spheroids in three-dimensional culture show a consistent up-regulation of p27 (up to 15-fold).35St Croix B Florenes VA Rak JW Flanagan M Bhattacharya N Slingerland JM Kerbel RS Impact of the cyclin-dependent kinase inhibitor p27kip1 on resistance of tumor cells to anti-cancer agents.Nature Med. 1996; 2: 1204-1210Crossref PubMed Scopus (303) Google Scholar When a mammary tumor cell line (EMT-6) was treated with antisense p27 oligonucleotides, there was increased cell proliferation, with restoration of the drug- or radiation-induced cell cycle perturbations that were repressed in spheroid culture.35St Croix B Florenes VA Rak JW Flanagan M Bhattacharya N Slingerland JM Kerbel RS Impact of the cyclin-dependent kinase inhibitor p27kip1 on resistance of tumor cells to anti-cancer agents.Nature Med. 1996; 2: 1204-1210Crossref PubMed Scopus (303) Google Scholar Recent studies have implicated p27 as a promoter of apoptosis.37Katayose Y Kim M Rakkar ANS Li Z Cowan KH Seth P Promoting ap