Downregulated CDKN1C/p57kip2 drives tumorigenesis and associates with poor overall survival in breast cancer

CIP/KIP and INK4 families as hostages of oncogenic signaling

CIP/KIP and INK4 families of Cyclin-dependent kinase inhibitors (CKIs) are well-established cell cycle regulatory proteins whose canonical function is binding to Cyclin-CDK complexes and altering their function. Initial experiments showed that these proteins negatively regulate cell cycle progression and thus are tumor suppressors in the context of molecular oncology. However, expanded research into the functions of these proteins showed that most of them have non-canonical functions, both cell cycle-dependent and independent, and can even act as tumor enhancers depending on their posttranslational modifications, subcellular localization, and cell state context. This review aims to provide an overview of canonical as well as non-canonical functions of CIP/KIP and INK4 families of CKIs, discuss the potential avenues to promote their tumor suppressor functions instead of tumor enhancing ones, and how they could be utilized to design improved treatment regimens for cancer patients.

Changes on chromosome 11p15.5 as specific marker for embryonal rhabdomyosarcoma?

Rhabdomyosarcomas (RMS) constitute a heterogeneous spectrum of tumors with respect to clinical behavior and tumor morphology. The paternal uniparental disomy (pUPD) of 11p15.5 is a molecular change described mainly in embryonal RMS. In addition to LOH, UPD, the MLPA technique (ME030kit) also determines copy number variants and methylation of H19 and KCNQ1OT1 genes, which have not been systematically investigated in RMS. All 127 RMS tumors were divided by histology and PAX status into four groups, pleomorphic histology (n = 2); alveolar RMS PAX fusion-positive (PAX+; n = 39); embryonal RMS (n = 70) and fusion-negative RMS with alveolar pattern (PAX-RMS-AP; n = 16). The following changes were detected; negative (n = 21), pUPD (n = 75), gain of paternal allele (n = 9), loss of maternal allele (n = 9), hypermethylation of H19 (n = 6), hypomethylation of KCNQ1OT1 (n = 6), and deletion of CDKN1C (n = 1). We have shown no difference in the frequency of pUPD 11p15.5 in all groups. Thus, we have proven that changes in the 11p15.5 are not only specific to the embryonal RMS (ERMS), but are often also present in alveolar RMS (ARMS). We have found changes that have not yet been described in RMS. We also demonstrated new potential diagnostic markers for ERMS (paternal duplication and UPD of whole chromosome 11) and for ARMS PAX+ (hypomethylation KCNQ1OT1).

Cyclin-dependent kinase inhibitors in malignant hematopoiesis

The cell-cycle is a tightly orchestrated process where sequential steps guarantee cellular growth linked to a correct DNA replication. The entire cell division is controlled by cyclin-dependent kinases (CDKs). CDK activation is balanced by the activating cyclins and CDK inhibitors whose correct expression, accumulation and degradation schedule the time-flow through the cell cycle phases. Dysregulation of the cell cycle regulatory proteins causes the loss of a controlled cell division and is inevitably linked to neoplastic transformation. Due to their function as cell-cycle brakes, CDK inhibitors are considered as tumor suppressors. The CDK inhibitors p16^INK4a and p15^INK4b are among the most frequently altered genes in cancer, including hematopoietic malignancies. Aberrant cell cycle regulation in hematopoietic stem cells (HSCs) bears severe consequences on hematopoiesis and provokes hematological disorders with a broad array of symptoms. In this review, we focus on the importance and prevalence of deregulated CDK inhibitors in hematological malignancies.

Functional regulations between genetic alteration-driven genes and drug target genes acting as prognostic biomarkers in breast cancer

Differences in genetic molecular features including mutation, copy number alterations and DNA methylation, can explain interindividual variability in response to anti-cancer drugs in cancer patients. However, identifying genetic alteration-driven genes and characterizing their functional mechanisms in different cancer types are still major challenges for cancer studies. Here, we systematically identified functional regulations between genetic alteration-driven genes and drug target genes and their potential prognostic roles in breast cancer. We identified two mutation and copy number-driven gene pairs (PARP1-ACSL1 and PARP1-SRD5A3), three DNA methylation-driven gene pairs (PRLR-CDKN1C, PRLR-PODXL2 and PRLR-SRD5A3), six gene pairs between mutation-driven genes and drug target genes (SLC19A1-SLC47A2, SLC19A1-SRD5A3, AKR1C3-SLC19A1, ABCB1-SRD5A3, NR3C2-SRD5A3 and AKR1C3-SRD5A3), and four copy number-driven gene pairs (ADIPOR2-SRD5A3, CASP12-SRD5A3, SLC39A11-SRD5A3 and GALNT2-SRD5A3) that all served as prognostic biomarkers of breast cancer. In particular, RARP1 was found to be upregulated by simultaneous copy number amplification and gene mutation. Copy number deletion and downregulated expression of ACSL1 and upregulation of SRD5A3 both were observed in breast cancers. Moreover, copy number deletion of ACSL1 was associated with increased resistance to PARP inhibitors. PARP1-ACSL1 pair significantly correlated with poor overall survival in breast cancer owing to the suppression of the MAPK, mTOR and NF-kB signaling pathways, which induces apoptosis, autophagy and prevents inflammatory processes. Loss of SRD5A3 expression was also associated with increased sensitivity to PARP inhibitors. The PARP1-SRD5A3 pair significantly correlated with poor overall survival in breast cancer through regulating androgen receptors to induce cell proliferation. These results demonstrate that genetic alteration-driven gene pairs might serve as potential biomarkers for the prognosis of breast cancer and facilitate the identification of combination therapeutic targets for breast cancers.

5-methylcytosine RNA methyltransferases and their potential roles in cancer

In recent years, 5-methylcytosine (m⁵C) RNA modification has emerged as a key player in regulating RNA metabolism and function through coding as well as non-coding RNAs. Accumulating evidence has shown that m⁵C modulates the stability, translation, transcription, nuclear export, and cleavage of RNAs to mediate cell proliferation, differentiation, apoptosis, stress responses, and other biological functions. In humans, m⁵C RNA modification is catalyzed by the NOL1/NOP2/sun (NSUN) family and DNA methyltransferase 2 (DNMT2). These RNA modifiers regulate the expression of multiple oncogenes such as fizzy-related-1, forkhead box protein C2, Grb associated-binding protein 2, and TEA domain transcription factor 1, facilitating the pathogenesis and progression of cancers. Furthermore, the aberrant expression of methyltransferases have been identified in various cancers and used to predict the prognosis of patients. In this review, we present a comprehensive overview of m⁵C RNA methyltransferases. We specifically highlight the potential mechanism of action of m⁵C in cancer. Finally, we discuss the prospect of m⁵C-relative studies.

Effects of tobacco compound 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on the expression of epigenetically regulated genes in lung carcinogenesis

Cigarette smoking is a major cause of lung cancer. Although tobacco smoking-induced genotoxicity has been well established, there is apparent lack of abundance functional epigenetic effects reported On cigarette smoke-induced lung carcinogenesis. The aim of this study was to determine effects of intratracheal administration of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) utilizing target gene expression DNA methylation patterns in lung tissues of mice following twice weekly for 8 weeks treatment. An unbiased approach where genomic regions was undertaken to assess early methylation changes within mouse pulmonary tissues. A methylated-CpG island recovery assay (MIRA) was performed to map the DNA methylome in lung tissues, with the position of methylated DNA determined using a Genome Analyzer (MIRA-SEQ). Alterations in epigenetic-regulated target genes were confirmed with quantitative reverse transcription-PCR, which revealed 35 differentially hypermethylated genes including Cdkn1C, Hsf4, Hnf1a, Cdx1, and Hoxa5 and 30 differentially hypomethylated genes including Ddx4, Piwi1, Mdm2, and Pce1 in NNK-exposed lung tissue compared with controls. The main pathway of these genes for mediating biological information was analyzed using the Kyoto Encyclopedia of Genes and Genomes database. Among them, Rssf1 and Mdm2 were closely associated with NNK-induced lung carcinogenesis. Taken together, our data provide valuable resources for detecting cigarette smoke-induced lung carcinogenesis.

Colonic Stent as Bridge to Surgery for Malignant Obstruction Induces Gene Expressional Changes Associated with a More Aggressive Tumor Phenotype

BACKGROUND

Colonic stent is recommended as a bridge to elective surgery for malignant obstruction to improve short-term clinical outcomes for patients with colorectal cancer. However, since the oncological outcomes remain controversial, this study aimed to investigate the impact of self-expandable metallic stent (SEMS) on the tumor microenvironment.

METHODS

Patients treated with colonic stent as a bridge to surgery from 2010 to 2015 were identified from hospital records. Tumor biopsies and resected tumor samples of the eligible patients were retrieved retrospectively. Gene expression analysis was performed using the NanoString nCounter PanCancer IO 360 gene expression panel.

RESULTS

Of the 164 patients identified, this study included 21 who underwent colonic stent placement as a bridge to elective surgery. Gene expression analysis revealed 82 differentially expressed genes between pre- and post-intervention specimens, of which 72 were upregulated and 10 downregulated. Among the significantly upregulated genes, 46 are known to have protumor functions, of which 26 are specifically known to induce tumorigenic mechanisms such as proliferation, migration, invasion, angiogenesis, and inflammation. In addition, ten differentially expressed genes were identified that are known to promote antitumor functions.

CONCLUSION

SEMS induces gene expressional changes in the tumor microenvironment that are associated with tumor progression in colorectal cancer and may potentiate a more aggressive phenotype. Future studies are warranted to establish optimal timing of surgery after SEMS insertion in patients with obstructive colorectal cancer.

CDKN1C as a prognostic biomarker correlated with immune infiltrates and therapeutic responses in breast cancer patients

Breast cancer (BC) prognosis and therapeutic sensitivity could not be predicted efficiently. Previous evidence have shown the vital roles of CDKN1C in BC. Therefore, we aimed to construct a CDKN1C‐based model to accurately predicting overall survival (OS) and treatment responses in BC patients. In this study, 995 BC patients from The Cancer Genome Atlas database were selected. Kaplan‐Meier curve, Gene set enrichment and immune infiltrates analyses were executed. We developed a novel CDKN1C‐based nomogram to predict the OS, verified by the time‐dependent receiver operating characteristic curve, calibration curve and decision curve. Therapeutic response prediction was followed based on the low‐ and high‐nomogram score groups. Our results indicated that low‐CDKN1C expression was associated with shorter OS and lower proportion of naïve B cells, CD8 T cells, activated NK cells. The predictive accuracy of the nomogram for 5‐year OS was superior to the tumour‐node‐metastasis stage (area under the curve: 0.746 vs. 0.634, p < 0.001). The nomogram exhibited excellent predictive performance, calibration ability and clinical utility. Moreover, low‐risk patients were identified with stronger sensitivity to therapeutic agents. This tool can improve BC prognosis and therapeutic responses prediction, thus guiding individualized treatment decisions.

CDKN1C-mediated growth inhibition by an EZH1/2 dual inhibitor overcomes resistance of mantle cell lymphoma to ibrutinib

Mantle cell lymphoma (MCL) is a rare subtype of non‐Hodgkin's lymphoma, which is characterized by overexpression of cyclin D1. Although novel drugs, such as ibrutinib, show promising clinical outcomes, relapsed MCL often acquires drug resistance. Therefore, alternative approaches for refractory and relapsed MCL are needed. Here, we examined whether a novel inhibitor of enhancer of zeste homologs 1 and 2 (EZH1/2), OR‐S1 (a close analog of the clinical‐stage compound valemetostat), had an antitumor effect on MCL cells. In an ibrutinib‐resistant MCL patient–derived xenograft (PDX) mouse model, OR‐S1 treatment by oral administration significantly inhibited MCL tumor growth, whereas ibrutinib did not. In vitro growth assays showed that compared with an established EZH2‐specific inhibitor GSK126, OR‐S1 had a marked antitumor effect on MCL cell lines. Furthermore, comprehensive gene expression analysis was performed using OR‐S1–sensitive or insensitive MCL cell lines and showed that OR‐S1 treatment modulated B‐cell activation, differentiation, and cell cycle. In addition, we identified Cyclin Dependent Kinase Inhibitor 1C (CDKN1C, also known as p57, KIP2), which contributes to cell cycle arrest, as a direct target of EZH1/2 and showed that its expression influenced MCL cell proliferation. These results suggest that EZH1/2 may be a potential novel target for the treatment of aggressive ibrutinib‐resistant MCL via CDKN1C‐mediated cell cycle arrest.

Immunoglobulin superfamily member 10 is a novel prognostic biomarker for breast cancer

Background

Immunoglobulin superfamily member 10 (IGSF10) is a member of the immunoglobulin superfamily that is expressed at high levels in both the gallbladder and ovary. Currently, the role and possible mechanism of IGSF10 in breast cancer remain unclear.

Method

By applying real-time quantitative polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC), the expression of IGSF10 in breast cancer cells and tissues was detected. We collected the clinical information from 700 patients with breast cancer in The Cancer Genome Atlas (TCGA), and analyzed the relationship between IGSF10 expression and the clinicopathological features and survival outcomes of these patients. The potential mechanisms and pathways associated with IGSF10 in breast cancer were explored by performing a gene set enrichment analysis (GSEA).

Results

According to TCGA data, qRT-PCR and IHC experiments, levels of the IGSF10 mRNA and protein were significantly decreased in breast cancer tissues. IGSF10 expression was significantly correlated with age, tumor size, and tumor stage. Moreover, shorter overall survival (OS) and relapse-free survival (RFS) correlated with lower IGSF10 expression, according to the survival analysis. The multivariate analysis identified that IGSF10 as an independent prognostic factor for the OS (hazard ratio (HR) = 1.793, 95% confidence interval (CI) [1.141–2.815], P = 0.011) and RFS (HR = 2.298, 95% CI [1.317–4.010], P = 0.003) of patients with breast cancer. Based on the GSEA, IGSF10 was involved in DNA repair, cell cycle, and glycolysis. IGSF10 was also associated with the PI3K/Akt/mTOR and mTORC1 signaling pathways.

Conclusions

This study revealed a clear relationship between IGSF10 expression and the tumorigenesis of breast cancer for the first time. Therefore, further studies are needed to understand the mechanism of IGSF10 in breast cancer.

Functional Versatility of the CDK Inhibitor p57Kip2

The cyclin/CDK inhibitor p57^Kip2 belongs to the Cip/Kip family, with p21^Cip1 and p27^Kip1, and is the least studied member of the family. Unlike the other family members, p57^Kip2 has a unique role during embryogenesis and is the only CDK inhibitor required for embryonic development. p57^Kip2 is encoded by the imprinted gene CDKN1C, which is the gene most frequently silenced or mutated in the genetic disorder Beckwith-Wiedemann syndrome (BWS), characterized by multiple developmental anomalies. Although initially identified as a cell cycle inhibitor based on its homology to other Cip/Kip family proteins, multiple novel functions have been ascribed to p57^Kip2 in recent years that participate in the control of various cellular processes, including apoptosis, migration and transcription. Here, we will review our current knowledge on p57^Kip2 structure, regulation, and its diverse functions during development and homeostasis, as well as its potential implication in the development of various pathologies, including cancer.

RNA methyltransferase NSUN2 promotes gastric cancer cell proliferation by repressing p57Kip2 by an m5C-dependent manner

The RNA methyltransferase NSUN2 has been involved in the cell proliferation and senescence, and is upregulated in various types of cancers. However, the role and potential mechanism of NSUN2 in gastric cancer remains to be determined. Our study showed that NSUN2 was significantly upregulated in gastric cancers, compared to adjacent normal gastric tissues. Moreover, NSUN2 could promote gastric cancer cell proliferation both in vitro and in vivo. Further study demonstrated that CDKN1C (p57^Kip2) was the potential downstream gene of regulated by NSUN2 in gastric cancer. NSUN2 could promote gastric cancer cell proliferation through repressing p57^Kip2 in an m⁵C-dependent manner. Our findings suggested that NSUN2 acted as an oncogene through promoting gastric cancer development by repressing p57^Kip2 in an m⁵C-dependent manner, which may provide a novel therapeutic target against gastric cancer.

Long non-coding RNA GAS5 accelerates oxidative stress in melanoma cells by rescuing EZH2-mediated CDKN1C downregulation

Background

The significance of long non-coding RNAs (lncRNAs) in mediating oxidative stress of cancers has been implicated recently. This study proposed a potential therapeutic target lncRNA growth arrest-specific transcript 5 (GAS5) for melanoma, due to its crucial role in oxidative stress and apoptosis of melanoma cells by regulating the enhancer of zeste homolog 2 (EZH2)-mediated CDKN1C expression.

Methods

The lncRNA GAS5 expression pattern was examined in melanoma tissues and cells. The correlation of lncRNA GAS5, EZH2, and CDKN1C with survival rate of melanoma patients was analyzed. In melanoma cell lines, lncRNA GAS5 expression was overexpressed or knocked down to clarify its effects on cell viability, apoptosis, and oxidative stress. The interaction between lncRNA GAS5 and EZH2 was examined by RIP and RNA pull-down assays followed by verification of the target relationship between EZH2 and CDKN1C.

Results

High expression of EZH2 and poor expression of lncRNA GAS5 and CDKN1C was observed in melanoma tissues and found to be correlated with the reduction in survival expectancy of melanoma patients. Overexpression of lncRNA GAS5 or CDKN1C or EZH2 knockdown could inhibit cell viability but enhance melanoma cell apoptosis and oxidative stress. Importantly, lncRNA GAS5 attenuated EZH2 expression by recruiting E2F4 to the EZH2 promoter region and knockdown of EZH2 upregulated CDKN1C expression by inhibiting the H3K27me3.

Conclusion

The evidence provided by our study highlighted the involvement of lncRNA GAS5 in the translational suppression of EZH2 as well as the upregulation of CDKN1C, resulting in the promotion of melanoma cell apoptosis and oxidative stress.

Systems Biology Integration and Screening of Reliable Prognostic Markers to Create Synergies in the Control of Lung Cancer Patients

This study aims to achieve a clearer and stronger understanding of all the mechanisms involved in the occurrence as well as in the progression of lung cancer along with discovering trustworthy prognostic markers. We combined four gene expression profiles (GSE19188, GSE19804, GSE101929, and GSE18842) from the GEO database and screened the commonly differentially expressed genes (CDEGs). We performed differentially expressed group analysis on CDEGs, alteration and mutational analysis, and expression level verification of core differential genes. Systems biology discoveries in our examination are predictable with past reports. Curiously, our examination revealed that screened biomarker adjustments, for the most part, coexist in lung cancer. After screening 952 CDEGs, we found that the up-regulation of neuromedin U (NMU) and GTSE1 in the case of lung cancer is related to poor prognosis. On the other hand, FOS CDKN1C expression is associated with poor prognosis and is responsible for the down-regulation of CDKN1C and FOS. Changes in these qualities are on free pathways to lung cancer and are not usually of combined quality variety. Even though biomarkers were related to both survival occasions in our examination, it gives us another point of view while playing out the investigation of hereditary changes and clinical highlights employing information mining. Based on our results, we found potential and prospective clinical applications in GTSE1, NMU, FOS, and CDKN1C to act as prognostic markers in case of lung cancer.

ATR-FTIR spectroscopy and CDKN1C gene expression in the prediction of lymph nodes metastases in papillary thyroid carcinoma

Thyroid cancer has become in recent years the most common endocrine malignancy. Among its different types, papillary thyroid carcinoma (PTC) has the highest incidence. PTC is slow growing, but shows a high rate of lymph node metastasis. Tissue biochemical characterization and identification of molecular markers can facilitate stratification of patients into those requiring surgical assessment of lymph nodes and patients for whom this surgical procedure is unnecessary; thus, leading to a more accurate prognosis. To this end, the study aimed to predict lymph node metastasis by Attenuated Total Reflectance - Fourier transform infrared (ATR-FTIR) spectroscopy of primary PTC tumors. Another objective of the study was to determine whether CCNA1, CDKN1C, FOS, HSPA5, JUN, KSR1, MAP2K6, MAPK8IP2 and SFN gene expression in primary PTC tumors could be used as predictive markers of lymph node metastasis. Three PTC with lymph node involvement (PTC+), six PTC without lymph node involvement (PTC-), and five normal (N) thyroid tissues were used for FTIR spectroscopy analysis; while 18 PTC+, 17 PTC-, and 6 N samples were used for molecular analysis by real-time quantitative PCR (RT-qPCR). FTIR spectral analysis revealed changes in phosphate groups possibly associated with nucleic acid (1236 cm^-1), and protein/lipids (1452, 2924, 3821 cm^-1) in PTC + compared to PTC-, and multivariate analysis could distinguish the two groups. Molecular analysis showed significant increase in CDKN1C gene expression in PTC + compared to PTC-. Being a cell growth regulator, increased CDKN1C provides some supporting evidence to the FTIR spectroscopy based finding of increased nucleic acids in PTC+. Thus, the study suggests the possibility of using FTIR spectroscopy and CDKN1C expression for predicting metastasis using primary tumor alone.

miR-221-3p Delivered by BMMSC-Derived Microvesicles Promotes the Development of Acute Myelocytic Leukemia

Objective: The study aims to investigate the effects of miR-221-3p in bone marrow mesenchymal stem cell (BMMSC)-derived microvesicles (MVs) on cell cycle, proliferation and invasion of acute myelocytic leukemia (AML).

Methods: Bioinformatics was used to predict differentially expressed miRNAs (DEmiRNAs) in AML. The morphology of BMMSC-derived MVs was observed under an electron microscope, and the positional relation of MVs and OCI-AML2 cells was observed by a fluorescence microscope. MTT, Transwell, and flow cytometry assays were used to analyze the effects of MVs on OCI-AML2 cells. The targeted relationship between miR-221-3p and CDKN1C was detected by dual luciferase assay.

Results: It was verified that miR-221-3p promoted the proliferation, invasion and migration of OCI-AML2 cells, and induced the cell cycle arrest in G1/S phase as well as inhibited cell apoptosis. Further studies showed that MVs promoted the proliferation, migration and invasion of AML, and induced the cell cycle arrest in G1/S phase through miR-221-3p. It was confirmed that miR-221-3p can directly target CDKN1C to regulate cell cycle, proliferation and invasion of AML.

Conclusion: miR-221-3p in BMMSC-derived MVs regulated AML cell cycle, cell proliferation and invasion through targeting CDKN1C. miR-221-3p and CDKN1C were considered to be potential targets and biomarkers for the treatment of AML in clinic.

LncRNA DANCR upregulates PI3K/AKT signaling through activating serine phosphorylation of RXRA

Conventional therapies and novel molecular targeted therapies against breast cancer have gained great advances over the past two decades. However, poor prognosis and low survival rate are far from expectation for improvement, particularly in patients with triple negative breast cancer (TNBC). Here, we found that lncRNA DANCR was significantly overregulated in TNBC tissues and cell lines compared with normal breast tissues or other type of breast cancer. Knockdown of DANCR suppressed TNBC proliferation both in vitro and in vivo. Further study of underlying mechanisms demonstrated that DANCR bound with RXRA and increased its serine 49/78 phosphorylation via GSK3β, resulting in activating PIK3CA transcription, and subsequently enhanced PI3K/AKT signaling and TNBC tumorigenesis. Taken together, Our findings identified DANCR as an pro-oncogene and uncoverd a new working pattern of lncRNA to mediate TNBC tumorigenesis, which may be a potential therapeutic target for improving treatment of TNBC.

Genetic and Epigenetic Control of CDKN1C Expression: Importance in Cell Commitment and Differentiation, Tissue Homeostasis and Human Diseases

The CDKN1C gene encodes the p57^Kip2 protein which has been identified as the third member of the CIP/Kip family, also including p27^Kip1 and p21^Cip1. In analogy with these proteins, p57^Kip2 is able to bind tightly and inhibit cyclin/cyclin-dependent kinase complexes and, in turn, modulate cell division cycle progression. For a long time, the main function of p57^Kip2 has been associated only to correct embryogenesis, since CDKN1C-ablated mice are not vital. Accordingly, it has been demonstrated that CDKN1C alterations cause three human hereditary syndromes, characterized by altered growth rate. Subsequently, the p57^Kip2 role in several cell phenotypes has been clearly assessed as well as its down-regulation in human cancers. CDKN1C lies in a genetic locus, 11p15.5, characterized by a remarkable regional imprinting that results in the transcription of only the maternal allele. The control of CDKN1C transcription is also linked to additional mechanisms, including DNA methylation and specific histone methylation/acetylation. Finally, long non-coding RNAs and miRNAs appear to play important roles in controlling p57^Kip2 levels. This review mostly represents an appraisal of the available data regarding the control of CDKN1C gene expression. In addition, the structure and function of p57^Kip2 protein are briefly described and correlated to human physiology and diseases.