CDK6 binds and promotes the degradation of the EYA2 protein

microRNA-155-5p initiates childhood acute lymphoblastic leukemia by regulating the IRF4/CDK6/CBL axis

Acute lymphoblastic leukemia (ALL) is a common malignancy in children. In this study, we aimed to explore putative mechanisms of microRNA-155-5p (miR-155-5p) involvement in childhood ALL (cALL) via interactions with casitas B-lineage lymphoma (CBL), interferon regulatory factor 4 (IRF4), and cyclin-dependent kinase 6 (CDK6). Bioinformatic analysis was performed initially to identify differentially expressed genes in cALL. The expression levels of miR-155-5p, CBL, IRF4, and CDK6 in peripheral blood lymphocytes from clinical ALL samples were determined using RT-qPCR and Western blot assays. A dual-luciferase reporter gene assay was used to ascertain a possible targeting relationship between miR-155-5p and CBL, CCK-8 assay and flow cytometry were used to measure cell activity and apoptosis of ALL cells. Co-IP was performed to investigate the interaction between CBL and IRF4 and the ubiquitination level of IRF4. Furthermore, in vivo validation was performed inducing xenograft tumor models with ALL cells in nude mice. As indicated by bioinformatic analysis, miR-155-5p and CDK6 were upregulated and CBL was downregulated in ALL. miR-155-5p was found to target CBL to inhibit CBL expression. miR-155-5p promoted the proliferation of ALL cells and inhibited their apoptosis by inhibiting the expression of CBL, which otherwise degraded IRF4 protein through ubiquitination, leading to inhibited CDK6 expression. Collectively, the results show that miR-155-5p can promote the development of cALL via the regulation on CBL-mediated IRF4/CDK6 axis.

The multi-functional eyes absent proteins

The Eyes Absent (EYA) proteins are the only known instance of a single polypeptide housing the following three separable biochemical activities: tyrosine phosphatase, threonine phosphatase, and transactivation. This uniquely positions the EYAs to participate in both transcriptional regulation and signal transduction pathways. But it also complicates the assignment of biological roles to individual biochemical activities through standard loss-of-function experiments. Nevertheless, there is an emerging literature linking developmental and pathological functions with the various EYA activities, and a growing list of disease states that might benefit from EYA-targeted therapeutics. There also remain multiple unresolved issues with significant implications for our understanding of how the EYAs might impact such ubiquitous signaling cascades as the MYC and Notch pathways. This review will describe the unique juxtaposition of biochemical activities in the EYAs, their interaction with signaling pathways and cellular processes, emerging evidence of roles in disease states, and the feasibility of therapeutic targeting of individual EYA activities. We will focus on the phosphatase activities of the vertebrate EYA proteins and will examine the current state of knowledge regarding: • substrates and signaling pathways affected by the EYA tyrosine phosphatase activity; • modes of regulation of the EYA tyrosine phosphatase activity; • signaling pathways that implicate the threonine phosphatase activity of the EYAs including a potential interaction with PP2A-B55α; • the interplay between the two phosphatase activities and the transactivation function of the EYAs; • disease states associated with the EYAs and the current state of development of EYA-targeted therapeutics.

SIX1 Activates STAT3 Signaling to Promote the Proliferation of Thyroid Carcinoma via EYA1

As a critical member of the Retinal Determination Gene Network (RDGN), SIX1 has been regarded as a tumor promoter in various types of cancer. However, its role in papillary thyroid carcinoma (PTC) has never been investigated. In this study, thyroid carcinoma tissue microarray staining was employed to identify the expression patterns of SIX1 and its co-activator EYA1. Papillary thyroid cancer cell lines, BCPAP, and TPC-1 cells were used to investigate the potential mechanism of SIX1 in vitro and in vivo. Flow cytometry analysis, MTT assay, the growth curve assay, colony formation assay, EdU incorporation and xenograft assay were performed to demonstrate the role of SIX1 in the malignant change of PTC cells. Western blot and Real-time PCR were used to detect the interaction among the SIX1, EYA1, and STAT3 signaling. In comparison with normal tissue, high expressions of SIX1 and EYA1 were associated with a malignant tumor. Importantly, SIX1 strongly correlated with EYA1 in thyroid carcinoma tissue microarray. Functional assays indicated SIX1 increased EYA1 expression by stabilizing EYA1 at the post-transcriptional level. Besides, SIX1 promoted the proliferation and invasion of thyroid carcinoma via activation of STAT3 signaling and its downstream targets in an EYA1-dependent manner. SIX1 can integrate with EYA1 to contribute to PTC development via activation of the classical STAT3 signaling. These data suggested targeting the abnormal activation of the SIX1/EYA1 complex may represent a novel therapeutic strategy for advanced PTC patients.

Targeting CDK6 in cancer: State of the art and new insights

Cyclin-dependent kinase 6 (CDK6) plays a vital role in regulating the progression of the cell cycle. More recently, CDK6 has also been shown to have a transcriptional role in tumor angiogenesis. Up-regulated CDK6 activity is associated with the development of several types of cancers. While CDK6 is over-expressed in cancer cells, it has a low detectable level in non-cancerous cells and CDK6-null mice develop normally, suggesting a specific oncogenic role of CDK6, and that its inhibition may represent an ideal mechanism-based and low toxic therapeutic strategy in cancer treatment. Identification of selective small molecule inhibitors of CDK6 is thus needed for drug development. Herein, we review the latest understandings of the biological regulation and oncogenic roles of CDK6. The potential clinical relevance of CDK6 inhibition, the progress in the development of small-molecule CDK6 inhibitors and the rational design of potential selective CDK6 inhibitors are also discussed.

Cyclin D3-dependent control of the dNTP pool and HIV-1 replication in human macrophages

Cyclins control the activation of cyclin-dependent kinases (CDK), which in turn, control the cell cycle and cell division. Intracellular availability of deoxynucleotides (dNTP) plays a fundamental role in cell cycle progression. SAM domain and HD domain-containing protein 1 (SAMHD1) degrades nucleotide triphosphates and controls the size of the dNTP pool. SAMHD1 activity appears to be controlled by CDK. Here, we show that knockdown of cyclin D3 a partner of CDK6 and E2 a partner of CDK2 had a major impact in SAMHD1 phosphorylation and inactivation and led to decreased dNTP levels and inhibition of HIV-1 at the reverse transcription step in primary human macrophages. The effect of cyclin D3 RNA interference was lost after degradation of SAMHD1 by HIV-2 Vpx, demonstrating the specificity of the mechanism. Cyclin D3 inhibition correlated with decreased activation of CDK2. Our results confirm the fundamental role of the CDK6-cyclin D3 pair in controlling CDK2-dependent SAMHD1 phosphorylation and dNTP pool in primary macrophages.

CDK6-a review of the past and a glimpse into the future: from cell-cycle control to transcriptional regulation

The G1 cell-cycle kinase CDK6 has long been thought of as a redundant homolog of CDK4. Although the two kinases have very similar roles in cell-cycle progression, it has recently become apparent that they differ in tissue-specific functions and contribute differently to tumor development. CDK6 is directly involved in transcription in tumor cells and in hematopoietic stem cells. These functions point to a role of CDK6 in tissue homeostasis and differentiation that is partially independent of CDK6's kinase activity and is not shared with CDK4. We review the literature on the contribution of CDK6 to transcription in an attempt to link the new findings on CDK6's transcriptional activity to cell-cycle progression. Finally, we note that anticancer therapies based on the inhibition of CDK6 kinase activity fail to take into account its kinase-independent role in tumor development.

The DACH/EYA/SIX gene network and its role in tumor initiation and progression

The functional abnormality of developmental genes is a common phenomenon in cancer initiation and progression. The retinal determination gene network (RDGN) is a key signal in Drosophila eye specification, and this conservative pathway is also required for the development of multiple organs in mammalian species. Recent studies demonstrated that aberrant expressions of RDGN components in vertebrates, mainly Dach, Six, and Eya, represent a novel tumor signal. RDGN regulates proliferation, apoptosis, tumor growth and metastasis through interactions with multiple signaling pathways in a co-ordinated fashion; Dach acts as a tumor suppressor, whereas Six and Eya function as oncogenes. Clinical analyses demonstrated that the expression levels of RDGN correlate with tumor stage, metastasis and survival, suggesting that combinational detection of this pathway might be used as a promising biomarker for the stratification of therapy and for the prediction of the prognosis of cancer patients.

Inhibition of microRNA-25 by tumor necrosis factor α is critical in the modulation of vascular smooth muscle cell proliferation

Atherosclerosis and coronary heart disease are characterized by a hyperplastic neointima and inflammation involving cytokines, such as tumor necrosis factor‑α (TNF‑α). TNF‑α is pleiotropic and mediates inflammation and proliferation in various cell types, such as vascular smooth muscle cells (VSMCs). The molecular mechanism for the pleiotropic effects of TNF‑α has not previously been fully elucidated. The current study identified that the expression of microRNA‑25 (miR‑25), a small noncoding RNA, was reduced in response to TNF‑α signaling in VSMCs. Restored miR‑25 expression inhibited cell proliferation and Ki‑67 expression. The present study indicated that cyclin‑dependent kinase 6 (CDK6) was the direct target gene of miR‑25 using mRNA and protein expression analysis, and luciferase assays. It was also observed that restored CDK6 expression in the miR‑25 mimic‑treated VSMCs partly reduced miR‑25‑mediated VSMC proliferation. In conclusion, miR‑25 is suggested to be important in TNF‑α‑induced abnormal proliferation of VSMCs.