MPP8 Governs the Activity of the LIF/STAT3 Pathway and Plays a Crucial Role in the Differentiation of Mouse Embryonic Stem Cells.

Mouse embryonic stem cells (mESCs) possess the remarkable characteristics of unlimited self-renewal and pluripotency, which render them highly valuable for both fundamental research and clinical applications. A comprehensive understanding of the molecular mechanisms underlying mESC function is of the utmost importance. The Human Silence Hub (HUSH) complex, comprising FAM208A, MPP8, and periphilin, constitutes an epigenetic silencing complex involved in suppressing retroviruses and transposons during early embryonic development. However, its precise role in regulating mESC pluripotency and differentiation remains elusive. In this study, we generated homogenous miniIAA7-tagged Mpp8 mouse ES cell lines. Upon induction of MPP8 protein degradation, we observed the impaired proliferation and reduced colony formation ability of mESCs. Furthermore, this study unveils the involvement of MPP8 in regulating the activity of the LIF/STAT3 signaling pathway and Nanog expression in mESCs. Finally, we provide compelling evidence that degradation of the MPP8 protein impairs the differentiation of mESC.

Co-transcriptional genome surveillance by HUSH is coupled to termination machinery.

The HUSH complex recognizes and silences foreign DNA such as viruses, transposons, and transgenes without prior exposure to its targets. Here, we show that endogenous targets of the HUSH complex fall into two distinct classes based on the presence or absence of H3K9me3. These classes are further distinguished by their transposon content and differential response to the loss of HUSH. A de novo genomic rearrangement at the Sox2 locus induces a switch from H3K9me3-independent to H3K9me3-associated HUSH targeting, resulting in silencing. We further demonstrate that HUSH interacts with the termination factor WDR82 and-via its component MPP8-with nascent RNA. HUSH accumulates at sites of high RNAPII occupancy including long exons and transcription termination sites in a manner dependent on WDR82 and CPSF. Together, our results uncover the functional diversity of HUSH targets and show that this vertebrate-specific complex exploits evolutionarily ancient transcription termination machinery for co-transcriptional chromatin targeting and genome surveillance.

Characterization of Hepatoma-Derived Growth Factor-Related Protein 2 Interactions with Heterochromatin.

The expression of genetic information is tightly controlled by chromatin regulatory proteins, including those in the heterochromatin gene repression family. Many of these regulatory proteins work together on the chromatin substrate to precisely regulate gene expression during mammalian development, giving rise to many different tissues in higher organisms from a fixed genomic template. Here we identify and characterize the interactions of two related heterochromatin regulatory proteins, heterochromatin protein 1 alpha (HP1α) and M-phase phosphoprotein 8 (MPP8), with hepatoma-derived growth factor-related protein 2 (HRP2). We find in biochemical experiments that HRP2 copurifies and co-sediments with heterochromatin-associated proteins, including HP1α and MPP8. Using the Chromatin in vivo Assay in multiple cell types, we demonstrate that HP1α-mediated gene repression dynamics are altered by the presence of HRP2. Furthermore, the knockout of HRP2 in MDA-MB-231 cells results in significant changes to chromatin structure and stability, which alter gene expression patterns. Here, we detail a mechanism by which HRP2 contributes to epigenetic transcriptional regulation through engagement with heterochromatin-associated proteins to stabilize the chromatin landscape and influence gene expression.

M-phase phosphoprotein 8 promotes gastric cancer growth and metastasis via p53/Bcl-2 and EMT-related signaling pathways.

BACKGROUND: The main issue of this study is to demonstrate whether M-phase phosphoprotein 8 (MPP8) affect gastric tumor growth and metastasis. METHODS: Retrospective study was proceeded in 280 patients' surgical specimens with different disease stages. Loss-of-function assays, including 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide, flow cytometry, and transwell assays were performed to evaluate the biological function of MPP8 in gastric cancer cells. Apoptosis and metastasis relative biomarkers were measured by quantitative real-time polymerase chain reaction and Western blot analysis. RESULTS: Compared with normal adjacent tissues, obviously elevated MPP8 expression was found in gastric cancer tissues. Elevated MPP8 expression was associated with male sex (vs female sex), intermediate differentiation (vs poorly differentiated cancer), and later stage (vs earlier stage). Furthermore, MPP8 overexpression in tumor tissues was marginally associated with a poor prognosis, with a significant relationship between MPP8 overexpression and prognosis among patients with poorly differentiated gastric cancer. Inhibition of MPP8 in these cells significantly suppressed proliferation and colony formation, promoted apoptosis, and repressed invasion. Furthermore, silencing of MPP8 remarkably increased apoptosis-related proteins (p53, Bax, and PARP) expression, but downregulated Bcl-2 expression. Silencing of MPP8 also decreased the expression of metastasis pathway-related proteins (N-cadherin and vimentin), and as well as the levels of anti-oncogene ZEB1, MET, and KRAS mRNA. CONCLUSION: Our findings demonstrated that MPP8 might be an oncogene by positively regulating gastric cancer cell function through the p53/Bcl-2 and epithelial to mesenchymal transition-related signaling pathways.

Tri-methylation of ATF7IP by G9a/GLP recruits the chromodomain protein MPP8.

BACKGROUND: G9a and the related enzyme GLP were originally identified as histone lysine methyltransferases and then shown to also methylate several other non-histone proteins. RESULTS: Here, we performed a comprehensive screen to identify their substrates in mouse embryonic stem cells (mESCs). We identified 59 proteins, including histones and other known substrates. One of the identified substrates, activating transcriptional factor 7-interacting protein 1 (ATF7IP), is tri-methylated at a histone H3 lysine 9 (H3K9)-like mimic by the G9a/GLP complex, although this complex mainly introduces di-methylation on H3K9 and DNA ligase 1 (LIG1) K126 in cells. The catalytic domain of G9a showed a higher affinity for di-methylated lysine on ATF7IP than LIG1, which may create different methylation levels of different substrates in cells. Furthermore, we found that M-phase phosphoprotein 8 (MPP8), known as a H3K9me3-binding protein, recognizes methylated ATF7IP via its chromodomain. MPP8 is also a known component of the human silencing hub complex that mediates silencing of transgenes via SETDB1 recruitment, which is a binding partner of ATF7IP. Although the interaction between ATF7IP and SETDB1 does not depend on ATF7IP methylation, we found that induction of SETDB1/MPP8-mediated reporter-provirus silencing is delayed in mESCs expressing only an un-methylatable mutant of ATF7IP. CONCLUSIONS: Our findings provide new insights into the roles of lysine methylation in non-histone substrates which are targeted by the G9a/GLP complex and suggest a potential function of ATF7IP methylation in SETDB1/MPP8-mediated transgene silencing.

Knockdown of MPP8 suppresses cell proliferation via regulation of HOXA5 in non-small cell lung cancer cells.

M-phase phosphoprotein 8 (MPP8) is reported to be closely implicated in cancer initiation and progression. In addition, the homeobox gene HOXA5 has been shown to play critical roles in hematopoiesis, embryogenesis, and tumorigenesis. Nevertheless, the functional relevance of MPP8 and it's relation with HOXA5 in non-small cell lung cancer (NSCLC) is unknown. Therefore, the present study aimed to detect the expression profile of MPP8 in NSCLC and further explore it's biological roles in lung cancer cells. Cell proliferation was measured by CCK-8 assay and EdU incorporation assay. Real-time PCR was applied to detect the mRNA expression of MPP8 and HOXA5. The protein levels of MPP8 and HOXA5 were evaluated by western blot. Our study found that the expression of MPP8 was significantly increased in the NSCLC tissue compared with the adjacent non-tumorous tissue. Compared with the human lung fibroblasts, the elevated gene expression of MPP8 was also detected in the human NSCLC cell lines including NCI-H23 and NCI-H1299. In addition, knockdown of MPP8 led to an obvious reduction in cell viability and DNA synthesis in NCI-H23 and NCI-H1299 cells. Furthermore, down-regulation of MPP8 resulted in elevated expression of HOXA5 in NSCLC cells both at the mRNA and protein levels. Moreover, depletion of HOXA5 abolished the anti-tumor function of MPP8 knockdown in NSCLC cells. The present study demonstrated that MPP8 was associated with NSCLC cell proliferation through regulation of HOXA5, suggesting that MPP8 may act as a novel therapeutic target for treatment of NSCLC.

Repression of M-phase phosphoprotein 8 inhibits melanoma growth and metastasis in vitro and in vivo.

Metastatic melanoma accounts for the majority of skin cancer deaths due to its aggressiveness and high resistance to current therapies. M-phase phosphoprotein 8 (MPP8) has been shown to bind to methylated H3K9 and promote tumor cell motility and invasion. The current study aimed to investigate the role of MPP8 in melanoma growth and metastasis. Our results showed that MMP8 was up-regulated in the metastatic melanoma specimens. Knockdown of MPP8 inhibited melanoma cell growth both in vitro and in vivo. Furthermore, down-regulation of MPP8 induced S-phase cell cycle arrest as well as altered expression of cell cycle-related proteins in melanoma cells. In addition, repression of MPP8 inhibited the migration and invasion of melanoma cells both in vitro and in vivo. Taken together, these data suggest that MPP8 knockdown could inhibit the growth and metastasis of melanoma cells and provide novel therapeutic target for melanoma treatment.

Lentivirus-mediated knockdown of M-phase phosphoprotein 8 inhibits proliferation of colon cancer cells.

M-phase phosphoprotein 8 (MPP8) has been reported to be overexpressed in various human carcinoma cells and was associated with tumor malignant characters. However, its functional role in colon cancer (CRC) is still unclear. In the present study, lentivirus-mediated short hairpin RNAs were designed to silence the MPP8 gene in CRC cells including RKO and SW1116 cells. The fluorescence microscopy was used to determine the knockdown efficiency of MPP8 by observing lentivirus-mediated green fluorescent protein expression. MPP8 expression in infected RKO and SW1116 was evaluated by real-time PCR and Western blot analysis. Cell proliferation was assessed by MTT assay and colony formation. Flow cytometry was applied to measure cell cycle and apoptosis. Transwell assay was used to determine the effect of MMP8 silencing on cell migration. Our results demonstrated that loss of MPP8 inhibited cell proliferation and migration and promoted cell apoptosis. These results indicate that MPP8 plays an important role in the proliferation and metastasis of CRC cells and suggest that silencing of MPP8 may be an effective therapeutic approach for the treatment of CRC.