Cyclin F-EXO1 axis controls cell cycle-dependent execution of double-strand break repair.

Ubiquitination is a crucial posttranslational modification required for the proper repair of DNA double-strand breaks (DSBs) induced by ionizing radiation (IR). DSBs are mainly repaired through homologous recombination (HR) when template DNA is present and nonhomologous end joining (NHEJ) in its absence. In addition, microhomology-mediated end joining (MMEJ) and single-strand annealing (SSA) provide backup DSBs repair pathways. However, the mechanisms controlling their use remain poorly understood. By using a high-resolution CRISPR screen of the ubiquitin system after IR, we systematically uncover genes required for cell survival and elucidate a critical role of the E3 ubiquitin ligase SCFcyclin F in cell cycle-dependent DSB repair. We show that SCFcyclin F-mediated EXO1 degradation prevents DNA end resection in mitosis, allowing MMEJ to take place. Moreover, we identify a conserved cyclin F recognition motif, distinct from the one used by other cyclins, with broad implications in cyclin specificity for cell cycle control.

BIG coordinates auxin and SHORT ROOT to promote asymmetric stem cell divisions in Arabidopsis roots.

KEY MESSAGE: BIG regulates ground tissue formative divisions by bridging the auxin gradient with SHR abundance in Arabidopsis roots. The formative divisions of cortex/endodermis initials (CEIs) and CEI daughter cells (CEIDs) in Arabidopsis roots are coordinately controlled by the longitudinal auxin gradient and the radial SHORT ROOT (SHR) abundance. However, the mechanism underlying this coordination remains poorly understood. In this study, we demonstrate that BIG regulates ground tissue formative divisions by bridging the auxin gradient with SHR abundance. Mutations in BIG gene repressed cell cycle progression, delaying the formative divisions within the ground tissues and impairing the establishment of endodermal and cortical identities. In addition, we uncovered auxin's suppressive effect on BIG expression, triggering CYCLIND6;1 (CYCD6;1) activation in an SHR-dependent fashion. Moreover, the degradation of RETINOBLASTOMA-RELATED (RBR) is jointly regulated by BIG and CYCD6;1. The loss of BIG function led to RBR protein accumulation, detrimentally impacting the SHR/SCARECROW (SCR) protein complex and the CEI/CEID formative divisions. Collectively, these findings shed light on a fundamental mechanism wherein BIG intricately coordinates the interplay between SHR/SCR and auxin, steering ground tissue patterning within Arabidopsis root tissue.

APC/C prevents a noncanonical order of cyclin/CDK activity to maintain CDK4/6 inhibitor-induced arrest.

Regulated cell cycle progression ensures homeostasis and prevents cancer. In proliferating cells, premature S phase entry is avoided by the E3 ubiquitin ligase anaphasepromoting complex/cyclosome (APC/C), although the APC/C substrates whose degradation restrains G1-S progression are not fully known. The APC/C is also active in arrested cells that exited the cell cycle, but it is not clear whether APC/C maintains all types of arrest. Here, by expressing the APC/C inhibitor, EMI1, we show that APC/C activity is essential to prevent S phase entry in cells arrested by pharmacological cyclin-dependent kinases 4 and 6 (CDK4/6) inhibition (Palbociclib). Thus, active protein degradation is required for arrest alongside repressed cell cycle gene expression. The mechanism of rapid and robust arrest bypass from inhibiting APC/C involves CDKs acting in an atypical order to inactivate retinoblastoma-mediated E2F repression. Inactivating APC/C first causes mitotic cyclin B accumulation which then promotes cyclin A expression. We propose that cyclin A is the key substrate for maintaining arrest because APC/C-resistant cyclin A, but not cyclin B, is sufficient to induce S phase entry. Cells bypassing arrest from CDK4/6 inhibition initiate DNA replication with severely reduced origin licensing. The simultaneous accumulation of S phase licensing inhibitors, such as cyclin A and geminin, with G1 licensing activators disrupts the normal order of G1-S progression. As a result, DNA synthesis and cell proliferation are profoundly impaired. Our findings predict that cancers with elevated EMI1 expression will tend to escape CDK4/6 inhibition into a premature, underlicensed S phase and suffer enhanced genome instability.

Injury-induced Foxm1 expression in the mouse kidney drives epithelial proliferation by a cyclin F-dependent mechanism.

Acute kidney injury (AKI) strongly upregulates the transcription factor Foxm1 in the proximal tubule in vivo, and Foxm1 drives epithelial proliferation in vitro. Here, we report that deletion of Foxm1 either with a nephron-specific Cre driver or by inducible global deletion reduced proximal tubule proliferation after ischemic injury in vivo. Foxm1 deletion led to increased AKI to chronic kidney disease transition, with enhanced fibrosis and ongoing tubule injury 6 weeks after injury. We report ERK mediated FOXM1 induction downstream of the EGFR in primary proximal tubule cells. We defined FOXM1 genomic binding sites by cleavage under targets and release using nuclease (CUT&RUN) and compared the genes located near FOXM1 binding sites with genes downregulated in primary proximal tubule cells after FOXM1 knockdown. The aligned data sets revealed the cell cycle regulator cyclin F (CCNF) as a putative FOXM1 target. We identified 2 cis regulatory elements that bound FOXM1 and regulated CCNF expression, demonstrating that Ccnf is strongly induced after kidney injury and that Foxm1 deletion abrogates Ccnf expression in vivo and in vitro. Knockdown of CCNF also reduced proximal tubule proliferation in vitro. These studies identify an ERK/FOXM1/CCNF signaling pathway that regulates injury-induced proximal tubule cell proliferation.

The Expression of Cell Cycle Cyclins in a Human Megakaryoblast Cell Line Exposed to Simulated Microgravity.

The study of the physiological and pathophysiological processes under extreme conditions facilitates a better understanding of the state of a healthy organism and can also shed light on the pathogenesis of diseases. In recent years, it has become evident that gravitational stress affects both the whole organism and individual cells. We have previously demonstrated that simulated microgravity inhibits proliferation, induces apoptosis, changes morphology, and alters the surface marker expression of megakaryoblast cell line MEG-01. In the present work, we investigate the expression of cell cycle cyclins in MEG-01 cells. We performed several experiments for 24 h, 72 h, 96 h and 168 h. Flow cytometry and Western blot analysis demonstrated that the main change in the levels of cyclins expression occurs under conditions of simulated microgravity after 96 h. Thus, the level of cyclin A expression showed an increase in the RPM group during the first 4 days, followed by a decrease, which, together with the peak of cyclin D, may indicate inhibition of the cell cycle in the G2 phase, before mitosis. In addition, based on the data obtained by PCR analysis, we were also able to see that both cyclin A and cyclin B expression showed a peak at 72 h, followed by a gradual decrease at 96 h. STED microscopy data also confirmed that the main change in cyclin expression of MEG-01 cells occurs at 96 h, under simulated microgravity conditions, compared to static control. These results suggested that the cell cycle disruption induced by RPM-simulated microgravity in MEG-01 cells may be associated with the altered expression of the main regulators of the cell cycle. Thus, these data implicate the development of cellular stress in MEG-01 cells, which may be important for proliferating human cells exposed to microgravity in real space.

Depletion of cap-binding protein eIF4E dysregulates amino acid metabolic gene expression.

Protein synthesis is metabolically costly and must be tightly coordinated with changing cellular needs and nutrient availability. The cap-binding protein eIF4E makes the earliest contact between mRNAs and the translation machinery, offering a key regulatory nexus. We acutely depleted this essential protein and found surprisingly modest effects on cell growth and recovery of protein synthesis. Paradoxically, impaired protein biosynthesis upregulated genes involved in the catabolism of aromatic amino acids simultaneously with the induction of the amino acid biosynthetic regulon driven by the integrated stress response factor GCN4. We further identified the translational control of Pho85 cyclin 5 (PCL5), a negative regulator of Gcn4, that provides a consistent protein-to-mRNA ratio under varied translation environments. This regulation depended in part on a uniquely long poly(A) tract in the PCL5 5' UTR and poly(A) binding protein. Collectively, these results highlight how eIF4E connects protein synthesis to metabolic gene regulation, uncovering mechanisms controlling translation during environmental challenges.

Whi5 hypo- and hyper-phosphorylation dynamics control cell-cycle entry and progression.

Progression through the cell cycle depends on the phosphorylation of key substrates by cyclin-dependent kinases. In budding yeast, these substrates include the transcriptional inhibitor Whi5 that regulates G1/S transition. In early G1 phase, Whi5 is hypo-phosphorylated and inhibits the Swi4/Swi6 (SBF) complex that promotes transcription of the cyclins CLN1 and CLN2. In late G1, Whi5 is rapidly hyper-phosphorylated by Cln1 and Cln2 in complex with the cyclin-dependent kinase Cdk1. This hyper-phosphorylation inactivates Whi5 and excludes it from the nucleus. Here, we set out to determine the molecular mechanisms responsible for Whi5's multi-site phosphorylation and how they regulate the cell cycle. To do this, we first identified the 19 Whi5 sites that are appreciably phosphorylated and then determined which of these sites are responsible for G1 hypo-phosphorylation. Mutation of 7 sites removed G1 hypo-phosphorylation, increased cell size, and delayed the G1/S transition. Moreover, the rapidity of Whi5 hyper-phosphorylation in late G1 depends on "priming" sites that dock the Cks1 subunit of Cln1,2-Cdk1 complexes. Hyper-phosphorylation is crucial for Whi5 nuclear export, normal cell size, full expression of SBF target genes, and timely progression through both the G1/S transition and S/G2/M phases. Thus, our work shows how Whi5 phosphorylation regulates the G1/S transition and how it is required for timely progression through S/G2/M phases and not only G1 as previously thought.

Translational control of MPS1 links protein synthesis with the initiation of cell division and spindle pole body duplication in Saccharomyces cerevisiae.

Protein synthesis underpins cell growth and controls when cells commit to a new round of cell division at a point in late G1 of the cell cycle called Start. Passage through Start also coincides with the duplication of the microtubule-organizing centers, the yeast spindle pole bodies, which will form the 2 poles of the mitotic spindle that segregates the chromosomes in mitosis. The conserved Mps1p kinase governs the duplication of the spindle pole body (SPB) in Saccharomyces cerevisiae. Here, we show that the MPS1 transcript has a short upstream open reading frame (uORF) that represses the synthesis of Mps1p. Mutating the MPS1 uORF makes the cells smaller, accelerates the appearance of Mps1p in late G1, and promotes completion of Start. Monitoring the SPB in the cell cycle using structured illumination microscopy revealed that mutating the MPS1 uORF enabled cells to duplicate their SPB earlier at a smaller cell size. The accelerated Start of MPS1 uORF mutants depends on the G1 cyclin Cln3p and the transcriptional repressor Whi5p but not on the Cln1,2p G1 cyclins. These results identify growth inputs in mechanisms that control duplication of the microtubule-organizing center and implicate these processes in the coupling of cell growth with division.

A Predictive Model Based on the FBXO Family Reveals the Significance of Cyclin F in Hepatocellular Carcinoma.

OBJECTIVE: The F-box protein (FBXO) family plays a key role in the malignant progression of tumors. However, the biological functions and clinical value of the FBXO family in liver cancer remain unclear. Our study comprehensively assessed the clinical value of the FBXO family in hepatocellular carcinoma (HCC) and constructed a novel signature based on the FBXO family to predict prognosis and guide precision immunotherapy. METHODS: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) databases were utilized to investigate the expression characteristics and prognostic value of the FBXO family in HCC. A predictive model based on the FBXO family using TCGA database; and its predictive ability was validated using the ICGC database. Further analyses revealed that this predictive model can independently predict the overall survival (OS) rate of patients with HCC. We further analyzed the association of this predictive model with signaling pathways, clinical pathological features, somatic mutations, and immune therapy responses. Finally, we validated the biological functions of cyclin F (CCNF) through in vitro experiments. RESULTS: A predictive model involving three genes (CCNF, FBXO43, and FBXO45) was constructed, effectively identifying high and low-risk patients with differences in OS, clinicopathological characteristics, somatic mutations, and immune cell infiltration status. Additionally, knock-down of CCNF in HCC cell lines reduced cell proliferation in vitro, suggesting that CCNF may be a potential therapeutic target for HCC. CONCLUSIONS: The predictive model based on the FBXO family can effectively predict OS and the immune therapy response in HCC. Additionally, CCNF is a potential therapeutic target for HCC.

The Crk4-Cyc4 complex regulates G2/M transition in Toxoplasma gondii.

A versatile division of apicomplexan parasites and a dearth of conserved regulators have hindered the progress of apicomplexan cell cycle studies. While most apicomplexans divide in a multinuclear fashion, Toxoplasma gondii tachyzoites divide in the traditional binary mode. We previously identified five Toxoplasma CDK-related kinases (Crk). Here, we investigated TgCrk4 and its cyclin partner TgCyc4. We demonstrated that TgCrk4 regulates conventional G2 phase processes, such as repression of chromosome rereplication and centrosome reduplication, and acts upstream of the spindle assembly checkpoint. The spatial TgCyc4 dynamics supported the TgCrk4-TgCyc4 complex role in the coordination of chromosome and centrosome cycles. We also identified a dominant TgCrk4-TgCyc4 complex interactor, TgiRD1 protein, related to DNA replication licensing factor CDT1 but played no role in licensing DNA replication in the G1 phase. Our results showed that TgiRD1 also plays a role in controlling chromosome and centrosome reduplication. Global phosphoproteome analyses identified TgCrk4 substrates, including TgORC4, TgCdc20, TgGCP2, and TgPP2ACA. Importantly, the phylogenetic and structural studies suggest the Crk4-Cyc4 complex is limited to a minor group of the binary dividing apicomplexans.

Overexpression of cyclin F/CCNF as an independent prognostic factor for poor survival in clear cell renal cell carcinoma.

Cyclin F (encoded by CCNF gene) has been reported to be implicated in the pathobiology of several human cancers. However, its potential clinical significance in clear cell renal cell carcinoma (ccRCC) remains unknown. The present study aimed to evaluate the potential significance of cyclin F, assessed by immunohistochemical (IHC) staining and molecular (bioinformatics) techniques, as a prognostic marker in ccRCC in relation to clinicopathological features and outcomes. IHC staining was performed using two independent ccRCC tissue array cohorts, herein called tissue macroarray (TMA)_1 and tissue microarray (TMA)_2, composed of 108 ccRCCs and 37 histologically normal tissues adjacent to the tumor (NAT) and 192 ccRCCs and 16 normal kidney samples, respectively. The mRNA expression data were obtained from The Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO) public datasets, followed by bioinformatics analysis of biological mechanisms underlying prognosis. The relationship between immune cell infiltration level and CCNF expression in ccRCC was investigated using the Tumor Immune Estimation Resource 2.0 (TIMER2) and Gene Expression Profiling Interactive Analysis 2 (GEPIA2). Cyclin F expression was significantly elevated in ccRCC lesions compared to both NAT and normal renal tissues. Likewise, CCNF mRNA was markedly increased in ccRCCs relative to non-cancerous tissues. In all analyzed cohorts, tumors with features of more aggressive behavior were more likely to display cyclin F/CCNF-high expression than low. Furthermore, patients with high cyclin F/CCNF expression had shorter overall survival (OS) times than those with low expression. In addition, multivariable analysis revealed that cyclin F/CCNF-high expression was an independent prognostic factor for poor OS in ccRCC. Enrichment analysis for mechanistically relevant processes showed that CCNF and its highly correlated genes initiate the signaling pathways that eventually result in uncontrolled cell proliferation. CCNF expression was also correlated with immune cell infiltration and caused poor outcomes depending on the abundance of tumor-infiltrating immune cells in ccRCC. Our findings suggest that cyclin F/CCNF expression is likely to have an essential role in ccRCC pathobiology through regulating multiple oncogenic signaling pathways and affecting the tumor immune microenvironment and may serve as prognostic biomarker and promising therapeutic target in ccRCC.

A systematic review on understanding the mechanistic pathways and clinical aspects of natural CDK inhibitors on cancer progression.: Unlocking cellular and biochemical mechanisms.

Cell division, differentiation, and controlled cell death are all regulated by phosphorylation, a key biological function. This mechanism is controlled by a variety of enzymes, with cyclin-dependent kinases (CDKs) being particularly important in phosphorylating proteins at serine and threonine sites. CDKs, which contain 20 unique components, serve an important role in regulating vital physiological functions such as cell cycle progression and gene transcription. Methodologically, an extensive literature search was performed using reputable databases such as PubMed, Google Scholar, Scopus, and Web of Science. Keywords encompassed "cyclin kinase," "cyclin dependent kinase inhibitors," "CDK inhibitors," "natural products," and "cancer therapy." The inclusion criteria, focused on relevance, publication date, and language, ensured a thorough representation of the most recent research in the field, encompassing articles published from January 2015 to September 2023. Categorization of CDKs into those regulating transcription and those orchestrating cell cycle phases provides a comprehensive understanding of their diverse functions. Ongoing clinical trials featuring CDK inhibitors, notably CDK7 and CDK4/6 inhibitors, illuminate their promising potential in various cancer treatments. This review undertakes a thorough investigation of CDK inhibitors derived from natural (marine, terrestrial, and peptide) sources. The aim of this study is to provide a comprehensive comprehension of the chemical classifications, origins, target CDKs, associated cancer types, and therapeutic applications.

Analysis of nondegradable cyclins reveals distinct roles of the mitotic cyclins in Drosophila meiosis.

Meiosis is a complex variant of the mitotic cell cycle, and as such relies on many of the same proteins involved in mitosis, but utilizes these in novel ways. As in mitosis, Cdk1 and its cyclin partners, Cyclin A, B, and B3 are required at multiple steps in meiosis. Here, we study the effect of stabilized forms of the three mitotic cyclins to study the consequences of failure to degrade the cyclins in meiosis. We find that stabilized Cyclin B3 promotes ectopic microtubule polymerization throughout the egg, dependent on APC/C activity and apparently due to the consequent destruction of Cyclin A and Cyclin B. We present data that suggests CycB, and possibly CycA, can also promote APC/C activity at specific stages of meiosis. We also present evidence that in meiosis APC/CCort and APC/CFzy are able to target Cyclin B via a novel degron. Overall, our findings highlight the distinct functions of the three mitotic Cdk-cyclin complexes in meiosis.

CDK-independent role of D-type cyclins in regulating DNA mismatch repair.

Although mismatch repair (MMR) is essential for correcting DNA replication errors, it can also recognize other lesions, such as oxidized bases. In G0 and G1, MMR is kept in check through unknown mechanisms as it is error-prone during these cell cycle phases. We show that in mammalian cells, D-type cyclins are recruited to sites of oxidative DNA damage in a PCNA- and p21-dependent manner. D-type cyclins inhibit the proteasomal degradation of p21, which competes with MMR proteins for binding to PCNA, thereby inhibiting MMR. The ability of D-type cyclins to limit MMR is CDK4- and CDK6-independent and is conserved in G0 and G1. At the G1/S transition, the timely, cullin-RING ubiquitin ligase (CRL)-dependent degradation of D-type cyclins and p21 enables MMR activity to efficiently repair DNA replication errors. Persistent expression of D-type cyclins during S-phase inhibits the binding of MMR proteins to PCNA, increases the mutational burden, and promotes microsatellite instability.

Functional characterization of D-type cyclins involved in cell division in rice.

BACKGROUND: D-type cyclins (CYCD) regulate the cell cycle G1/S transition and are thus closely involved in cell cycle progression. However, little is known about their functions in rice. RESULTS: We identified 14 CYCD genes in the rice genome and confirmed the presence of characteristic cyclin domains in each. The expression of the OsCYCD genes in different tissues was investigated. Most OsCYCD genes were expressed at least in one of the analyzed tissues, with varying degrees of expression. Ten OsCYCD proteins could interact with both retinoblastoma-related protein (RBR) and A-type cyclin-dependent kinases (CDKA) forming holistic complexes, while OsCYCD3;1, OsCYCD6;1, and OsCYCD7;1 bound only one component, and OsCYCD4;2 bound to neither protein. Interestingly, all OsCYCD genes except OsCYCD7;1, were able to induce tobacco pavement cells to re-enter mitosis with different efficiencies. Transgenic rice plants overexpressing OsCYCD2;2, OsCYCD6;1, and OsCYCD7;1 (which induced cell division in tobacco with high-, low-, and zero-efficiency, respectively) were created. Higher levels of cell division were observed in both the stomatal lineage and epidermal cells of the OsCYCD2;2- and OsCYCD6;1-overexpressing plants, with lower levels seen in OsCYCD7;1-overexpressing plants. CONCLUSIONS: The distinct expression patterns and varying effects on the cell cycle suggest different functions for the various OsCYCD proteins. Our findings will enhance understanding of the CYCD family in rice and provide a preliminary foundation for the future functional verification of these genes.

The CDK Pho85 inhibits Whi7 Start repressor to promote cell cycle entry in budding yeast.

Pho85 is a multifunctional CDK that signals to the cell when environmental conditions are favorable. It has been connected to cell cycle control, mainly in Start where it promotes the G1/S transition. Here we describe that the Start repressor Whi7 is a key target of Pho85 in the regulation of cell cycle entry. The phosphorylation of Whi7 by Pho85 inhibits the repressor and explains most of the contribution of the CDK in the activation of Start. Mechanistically, Pho85 downregulates Whi7 protein levels through the control of Whi7 protein stability and WHI7 gene transcription. Whi7 phosphorylation by Pho85 also restrains the intrinsic ability of Whi7 to associate with promoters. Furthermore, although Whi5 is the main Start repressor in normal cycling cells, in the absence of Pho85, Whi7 becomes the major repressor leading to G1 arrest. Overall, our results reveal a novel mechanism by which Pho85 promotes Start through the regulation of the Whi7 repressor at multiple levels, which may confer to Whi7 a functional specialization to connect the response to adverse conditions with the cell cycle control.

Cyclin F can alter the turnover of TDP-43.

Previously, we demonstrated that the SCFcyclin F complex directly mediates the poly-ubiquitylation of TDP-43, raising the question of whether cyclin F can be used to enhance the turnover of TDP-43. A hurdle to the use of cyclin F, however, is that the overexpression of cyclin F can lead to the initiation of cell death pathways. Accordingly, the aim of this study was to identify and evaluate a less toxic variant of cyclin F. To do so, we first confirmed and validated our previous findings that cyclin F binds to TDP-43 in an atypical manner. Additionally, we demonstrated that mutating the canonical substrate region in cyclin F (to generate cyclin FMRL/AAA) led to reduced binding affinity to known canonical substrates without impacting the interaction between cyclin F and TDP-43. Notably, both wild-type and cyclin FMRL/AAA effectively reduced the abundance of TDP-43 in cultured cells whilst cyclin FMRL/AAA also demonstrated reduced cell death compared to the wild-type control. The decrease in toxicity also led to a reduction in morphological defects in zebrafish embryos. These results suggest that cyclin F can be modified to enhance its targeting of TDP-43, which in turn reduces the toxicity associated with the overexpression of cyclin F. This study provides greater insights into the interaction that occurs between cyclin F and TDP-43 in cells and in vivo.

Inhibition of the Cyclin K-CDK12 complex induces DNA damage and increases the effect of androgen deprivation therapy in prostate cancer.

Androgen deprivation therapy (ADT) is the mainstay of the current first-line treatment concepts for patients with advanced prostate carcinoma (PCa). However, due to treatment failure and recurrence investigation of new targeted therapeutics is urgently needed. In this study, we investigated the suitability of the Cyclin K-CDK12 complex as a novel therapeutic approach in PCa using the new covalent CDK12/13 inhibitor THZ531. Here we show that THZ531 impairs cellular proliferation, induces apoptosis, and decreases the expression of selected DNA repair genes in PCa cell lines, which is associated with an increasing extent of DNA damage. Furthermore, combination of THZ531 and ADT leads to an increase in these anti-tumoral effects in androgen-sensitive PCa cells. The anti-proliferative and pro-apoptotic activity of THZ531 in combination with ADT was validated in an ex vivo PCa tissue culture model. In a retrospective immunohistochemical analysis of 300 clinical tissue samples we show that Cyclin K (CycK) but not CDK12 expression correlates with a more aggressive type of PCa. In conclusion, this study demonstrates the clinical relevance of the CycK-CDK12 complex as a promising target for combinational therapy with ADT in PCa and its importance as a prognostic biomarker for patients with PCa.

Alternative cleavage and polyadenylation of the Ccnb1 mRNA defines accumulation of cyclin protein during the meiotic cell cycle.

Progression through the mitotic and meiotic cell cycle is driven by fluctuations in the levels of cyclins, the regulatory subunits controlling the localization and activity of CDK1 kinases. Cyclin levels are regulated through a precise balance of synthesis and degradation. Here we demonstrate that the synthesis of Cyclin B1 during the oocyte meiotic cell cycle is defined by the selective translation of mRNA variants generated through alternative cleavage and polyadenylation (APA). Using gene editing in mice, we introduced mutations into the proximal and distal polyadenylation elements of the 3' untranslated region (UTR) of the Ccnb1 mRNA. Through in vivo loss-of-function experiments, we demonstrate that the translation of mRNA with a short 3' UTR specifies Cyclin B1 protein levels that set the timing of meiotic re-entry. In contrast, translation directed by a long 3' UTR is necessary to direct Cyclin B1 protein accumulation during the MI/MII transition. These findings establish that the progression through the cell cycle is dependent on the selective translation of multiple mRNA variants generated by APA.

Beyond cell cycle regulation: The pleiotropic function of CDK4 in cancer.

CDK4, along with its regulatory subunit, cyclin D, drives the transition from G1 to S phase, during which DNA replication and metabolic activation occur. In this canonical pathway, CDK4 is essentially a transcriptional regulator that acts through phosphorylation of retinoblastoma protein (RB) and subsequent activation of the transcription factor E2F, ultimately triggering the expression of genes involved in DNA synthesis and cell cycle progression to S phase. In this review, we focus on the newly reported functions of CDK4, which go beyond direct regulation of the cell cycle. In particular, we describe the extranuclear roles of CDK4, including its roles in the regulation of metabolism, cell fate, cell dynamics and the tumor microenvironment. We describe direct phosphorylation targets of CDK4 and decipher how CDK4 influences these physiological processes in the context of cancer.