p27Kip1 inhibits cyclin D-cyclin-dependent kinase 4 by two independent modes
Authors: Stacy W Blain
Robert P Fisher
Arpita Ray
Stéphane Larochelle
Melissa K James
Journal: Molecular and cellular biology (2009)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: Cell cycle progression; cyclin-dependent kinases; p27(Kip1); tyrosine phosphorylation; cyclin D-cyclin-dependent kinase 4 (cdk4)
Affiliations: Program in Molecular and Cellular Biology, School of Graduate Studies, Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, Departments of Pediatrics and Anatomy and Cell Biology, SUNY Downstate Medical Center, Brooklyn, New York 11203

Abstract:  Cell cycle progression is regulated by cyclin-dependent kinases (cdk's), which in turn are regulated by their interactions with stoichiometric inhibitors, such as p27(Kip1). Although p27 associates with cyclin D-cyclin-dependent kinase 4 (cdk4) constitutively, whether or not it inhibits this complex is dependent on the absence or presence of a specific tyrosine phosphorylation that converts p27 from a bound inhibitor to a bound noninhibitor under different growth conditions. This phosphorylation occurs within the 3-10 helix of p27 and may dislodge the helix from cdk4's active site to allow ATP binding. Here we show that the interaction of nonphosphorylated p27 with cdk4 also prevents the activating phosphorylation of the T-loop by cyclin H-cdk7, the cdk-activating kinase (CAK). Even though the cyclin H-cdk7 complex is present and active in contact-arrested cells, p27's association with cyclin D-cdk4 prevents T-loop phosphorylation. When p27 is tyrosine phosphorylated in proliferating cells or in vitro with the tyrosine Y kinase Abl, phosphorylation of cdk4 by cyclin H-cdk7 is permitted, even without dissociation of p27. This suggests that upon release from the contact-arrested state, a temporal order for the reactivation of inactive p27-cyclin D-cdk4 complexes must exist: p27 must be Y phosphorylated first, directly permitting cyclin H-cdk7 phosphorylation of residue T172 and the consequent restoration of kinase activity. The non-Y-phosphorylated p27-cyclin D-cdk4 complex could be phosphorylated by purified Csk1, a single-subunit CAK from fission yeast, but was still inactive due to p27's occlusion of the active site. Thus, the two modes by which p27 inhibits cyclin D-cdk4 are independent and may reinforce one another to inhibit kinase activity in contact-arrested cells, while maintaining a reservoir of preformed complex that can be activated rapidly upon cell cycle reentry. 

Retracted: No

PubPeer comments:
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 Figure 2B. Much more similar than you would expect. https: imgur.com eSC4Evp , 
 22 Aug 2022 Expression of Concern. https: journals.asm.org doi 10.1128 mcb.00324-22 The American Society for Microbiology (ASM) and Molecular and Cellular Biology (MCB) are issuing this Expression of Concern regarding the following publication: Ray A, James MK, Larochelle S, Fisher RP, Blain SW. 2009. p27Kip1 inhibits cyclin Du2013cyclin-dependent kinase 4 by two independent modes. Mol Cell Biol 29(4):986u2013999. https: doi.org 10.1128 MCB.00898-08. Molecular and Cellular Biology was notified that the above-mentioned paper was investigated by the SUNY Downstate Health Sciences University and that potential image duplications were found in Fig. 3A. This Expression of Concern is issued pending the outcome of ongoing litigation between SUNY Downstate Health Sciences University and the corresponding author of the paper, Stacy Blain, in the U.S. District Court of the Eastern District of New York. , 
 #4 https: ia802504.us.archive.org 22 items gov.uscourts.nyed.480260 gov.uscourts.nyed.480260.1.0.pdf , 
 https: retractionwatch.com 2022 08 25 exclusive-cancer-researcher-sues-med-school-for-retaliation-after-research-misconduct-finding , 
 An additional concern about Figure 6: * Red boxes: Three lanes in the Ip cdk4, p27* panel of Figure 6D look very similar to three lanes in the cdk4* panel of Figure 6E. ![file] ,