Rab20 and Rab30 regulate hepatocellular carcinoma (HCC) for tumor suppression

Abstract

Ras related in brain 20 (Rab20) and Ras related in brain 30 (Rab30) are members of the Rab family of small GTP-binding proteins. Rab proteins contribute to the control of vesicular traffic in eukaryotic cells, by which they mainly regulate the precision of vesicle transportation along the biosynthesis/secretary pathway. Rab20 and Rab30 are low-weight GTPase that localise in the Golgi apparatus. Rab20 participates in apical endocytosis and phagosome functions, while Rab30 is important for controlling the structural integrity of the Golgi apparatus. Functions of Rab20/30 in cancer development have not been fully understood. Rab20 was identified to be upregulated in pancreatic cancer, and should be associated wih early stage of pancreatic carcinogenesis. However, roles of Rab30 has not been published in any cancer research. This drives us to investigate the potential roles of Rab20/30 in the development of hepatocellular carcinoma (HCC). In order to evaluvate the expression of Rab20 and Rab30 in HCC, 30 clinical cases were randomly selected for Real-time quantitative PCR using Rab20/30 TaqMan Gene Expression Assays (Applied Biosystem®). HPRT was selected as the internal control for normalization. Clinicopathological correlation and statistical analysis were performed to determine their expression ratios of tumorous to non-tumorous samples and potential roles in HCC development. Expessions of Rab20/30 were also determined in nine HCC cell lines through qPCR. Selected cell lines included MIHA, BEL7402, Hep3B, HLE, Huh7, PLC/PRF/5, SMMC7721, MHCC97L and MHCC-LM3. Our qPCR results reflected both Rab20 and Rab30 were significantly down-regulated in tumorous samples when compared to non-tumourous samples, with the p-value of 0.0115 and 0.0004, respectively. Regarding to tumor stage, underexpresssion of Rab20 was mainly observed in patients with stage III-IV, which is regarded as late stage. In contrast, apart from patients with stage III-IV, underexpression of Rab30 was also detected in patients with stage I-II. This suggested Rab20 maybe responsible for HCC progression by inhibiting invasive and metastatic properties of HCC, while Rab30 may play roles in the initiation of hepatocarcinogenesis. None of the clinicopathological parameters tested was significantly associated to the expression of Rab20/30. For HCC cell line panel, Rab20 was highly expressed in MIHA and BEL7402, but slightly expressed in other cell lines. There was no obvious expression pattern of Rab30 in HCC cell lines. Through qPCR, Rab20 and Rab30 were underexpressed in HCC, implying their potenital role in tumor suppression. Rab20 was mainly down-regulated in late stages, while underexpression of Rab30 may be an early event in hepatocarcinogenesis. Further experiments were needed to determine the functional significance of Rab20/30 in HCC initiation and progression.