Department of Precision Medicine, University of Campania "Luigi Vanvitelli", 80138 Naples, Italy.
Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy.
Int J Mol Sci. 2024 Oct 17;25(20):11176. doi: 10.3390/ijms252011176.
p57 is a member of the cyclin-dependent kinase (CDK) Interacting Protein/Kinase Inhibitory Protein (CIP/Kip) family that also includes p21 and p27. Different from its siblings, few data are available about the p57 protein, especially in humans. Structurally, p57 is an intrinsically unstructured protein, a characteristic that confers functional flexibility with multiple transient interactions influencing the metabolism and roles of the protein. Being an IUP, its localization, stability, and binding to functional partners might be strongly modulated by post-translational modifications, especially phosphorylation. In this work, we investigated by two-dimensional analysis the phosphorylation pattern of p57 in different cellular models, revealing how the human protein appears to be extensively phosphorylated, compared to p21 and p27. We further observed clear differences in the phosphoisoforms distributed in the cytosolic and nuclear compartments in asynchronous and synchronized cells. Particularly, the unmodified form is detectable only in the nucleus, while the more acidic forms are present in the cytoplasm. Most importantly, we found that the phosphorylation state of p57 influences the binding with some p57 partners, such as CDKs, LIMK1 and CRM1. Thus, it is necessary to completely identify the phosphorylated residues of the protein to fully unravel the roles of this CIP/Kip protein, which are still partially identified.
p57 是细胞周期蛋白依赖性激酶 (CDK) 相互作用蛋白/激酶抑制蛋白 (CIP/Kip) 家族的成员，该家族还包括 p21 和 p27。与它的兄弟姐妹不同，关于 p57 蛋白的数据很少，特别是在人类中。从结构上讲，p57 是一种固有无结构的蛋白质，这种特性赋予了它多功能的灵活性，通过多种瞬时相互作用影响蛋白质的代谢和功能。作为 IUP，其定位、稳定性和与功能伙伴的结合可能受到翻译后修饰的强烈调节，特别是磷酸化。在这项工作中，我们通过二维分析研究了 p57 在不同细胞模型中的磷酸化模式，揭示了与 p21 和 p27 相比，人类蛋白似乎广泛磷酸化。我们还观察到在不同步和同步细胞中，细胞质和核质部分的磷酸化异构体分布存在明显差异。特别是，未经修饰的形式仅在核内可检测到，而更酸性的形式存在于细胞质中。最重要的是，我们发现 p57 的磷酸化状态会影响与某些 p57 伙伴（如 CDK、LIMK1 和 CRM1）的结合。因此，有必要完全鉴定该蛋白的磷酸化残基，以充分阐明该 CIP/Kip 蛋白的作用，这些作用仍部分确定。
