Department of Hepatobiliary Surgery, The Third Affiliated Hospital, The Third Military Medical University (Army medical university), Chongqing, China.
Sci Rep. 2018 Jul 2;8(1):9917. doi: 10.1038/s41598-018-28339-4.
Transmembrane and ubiquitin-like domain-containing 1 (Tmub1) encodes a protein (TMUB1) containing an ubiquitin-like domain and plays a negative regulatory role during hepatocyte proliferation, but its mechanism in this process is still unknown. Here, TMUB1 interfered with the binding of calcium-modulating cyclophilin ligand (CAML) to cyclophilin B, which may represent a key role in the negative regulatory process of TMUB1 in hepatocyte proliferation. Co-immunoprecipitation assays in rat BRL-3A cells confirmed the interaction between TMUB1 and CAML; significant regulation of the influx of Ca2+ ([Ca2+]i) and hepatocyte proliferation occurred following TMUB1 overexpression or knockout. Deletion of the TM1 hydrophobic domain of TMUB1 completely abolished this interaction and led to loss of TMUB1's regulatory effects on cytological behavior. Furthermore, overexpression of TMUB1 completely abolished the interaction between CAML and its downstream protein cyclophilin B, which can act upstream of calcineurin by increasing [Ca2+]i during cell proliferation. Taken together, our results indicate that TMUB1 regulates BRL-3A hepatocyte proliferation by interacting with CAML and further interferes with the binding of CAML to cyclophilin B to decrease cellular [Ca2+]i.
跨膜和泛素样结构域蛋白 1（TMUB1）编码一种含有泛素样结构域的蛋白质（TMUB1），在肝细胞增殖过程中发挥负调控作用，但在该过程中其机制尚不清楚。在这里，TMUB1 干扰钙调节亲环素配体（CAML）与亲环素 B 的结合，这可能代表 TMUB1 在肝细胞增殖的负调控过程中的一个关键作用。在大鼠 BRL-3A 细胞中的共免疫沉淀实验证实了 TMUB1 和 CAML 之间的相互作用；TMUB1 过表达或敲除后，Ca2+（[Ca2+]i）内流和肝细胞增殖均发生显著调节。TMUB1 的 TM1 疏水区域的缺失完全消除了这种相互作用，并导致 TMUB1 对细胞行为的调节作用丧失。此外，TMUB1 的过表达完全消除了 CAML 与其下游蛋白亲环素 B 之间的相互作用，该作用可通过在细胞增殖过程中增加[Ca2+]i 来作用于钙调神经磷酸酶的上游。总之，我们的研究结果表明，TMUB1 通过与 CAML 相互作用来调节 BRL-3A 肝细胞的增殖，并进一步干扰 CAML 与亲环素 B 的结合，从而降低细胞内[Ca2+]i。
