TMUB1 Inhibits BRL-3A Hepatocyte Proliferation by Interfering with the Binding of CAML to Cyclophilin B through its TM1 Hydrophobic Domain

The Ins and Outs of HOPS/TMUB1 in biology and pathology

Liver regeneration represents an outstanding tool to study not only proliferation, but also other important processes such as inflammation, regenerative response or stem cell biology. Several novel genes have been identified as being involved in the proliferation of residual hepatocytes. One of them, HOPS/TMUB1, is proving to be a significant player in the control of proliferation, both contributing to genomic stability and as a partner of essential molecules. HOPS is an ubiquitin-like protein, shuttling from nucleus to cytoplasm, and it is engaged in a number of biological and physiopathological functions. HOPS overexpression in tumour cell lines strongly reduces proliferation, arresting cell cycle in G₀ /G₁ . HOPS is involved in centrosome assembly and maintenance, and its knockdown causes genomic instability. Moreover, a direct interaction of HOPS with nucleophosmin (NPM) and p19^Arf has been established, resulting in proper control of p19^Arf stability and localization. These data indicate that HOPS acts as a functional bridge in the interaction between NPM and p19^Arf , providing new mechanistic insight into how NPM and p19^Arf will oppose cell proliferation. HOPS exerts a control in p53 stability, directing p53 mitochondrial apoptosis and cytoplasmic localization. HOPS plays a direct role as novel post-translational modifier of p53, much like SUMO or NEDD. HOPS is overexpressed in a high number of human tumours in patients affected by large intestinal, CNS, liver and oesophageal tumours. This review highlights HOPS involvement in distinct cellular functions, establishing its role as a key player in cell biology and pathology in a broader context.

Transmembrane and Ubiquitin-Like Domain Containing 1 Protein (TMUB1) Negatively Regulates Hepatocellular Carcinoma Proliferation via Regulating Signal Transducer and Activator of Transcription 1 (STAT1)

Background

Hepatocellular carcinoma (HCC) is a common malignancy, but the pathogenesis of HCC is unclear. TMUB1 has an inhibitory effect on normal hepatocytes, but its role in HCC has not been reported.

Material/Methods

We used immunohistochemistry to observe the expression of transmembrane and ubiquitin-like domain containing 1 protein (TMUB1) and signal transducer and activator of transcription 1 (STAT1) in 132 HCC tissue specimens. The expression of TMUB1, STAT1, and CCND1 in HCC cells were detected by quantitative polymerase chain reaction (qPCR) and western blotting. Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2′-deoxyuridine (EdU) assays were used for detecting HCC cells proliferation, and Transwell assays were used for observing the invasion and migration of HCC cells.

Results

TMUB1 was negatively correlated with HCC pathological malignancy; low expression of TMUB1 indicated poor prognosis. TMUB1 inhibited proliferation but not metastasis in HCC cells. TMUB1 expression was positively correlated with STAT1 in 132 HCC tissues, TMUB1 promoted the expression of STAT1, and suppressed the expression of CCND1 in HCC cells.

Conclusions

TMUB1 negatively regulates hepatocellular carcinoma proliferation via regulating STAT1.

Tmub1 negatively regulates liver regeneration via inhibiting STAT3 phosphorylation

Tmub1 (transmembrane and ubiquitin-like domain-containing 1) plays negative roles in rat hepatocyte proliferation, but its underlying molecular mechanisms in liver regeneration regulation have yet to be revealed. Here, we show that in vivo transfection of Tmub1 overexpression vectors impaired mouse liver regeneration after partial hepatectomy (PHx). Loss- and gain-of-function analyses in human hepatocyte Lo2 cells indicated that Tmub1 inhibits the phosphorylation of STAT3 and the activation of STAT3 signaling. Furthermore, the inhibitory effect of Tmub1 overexpression on hepatocyte proliferation can be reversed by the STAT3 activator OSM, while the promotive effect of Tmub1 knockdown can be abolished by the STAT3 inhibitor stattic. Coimmunoprecipitation assays revealed interaction between Tmub1 and STAT3. Finally, we present data from chromatin immunoprecipitation and luciferase reporter gene assays and report that STAT3 binds to and activates the promoter of Tmub1, suggesting a putative negative feedback loop between Tmub1 and STAT3 signaling. Taken together, the results of our study suggest that Tmub1 is an important negative regulator of hepatocyte proliferation in liver regeneration through STAT3 signaling. These findings provide a potential strategy for the management of liver regeneration.