GRAMD4 inhibits tumour metastasis by recruiting the E3 ligase ITCH to target TAK1 for degradation in hepatocellular carcinoma

BACKGROUND

Aberrant TAK1 (transforming growth factor β-activated kinase 1) activity is known to be involved in a variety of malignancies, but the regulatory mechanisms of TAK1 remain poorly understood. GRAMD4 (glucosyltransferase Rab-like GTPase activator and myotubularin domain containing 4) is a newly discovered p53-independent proapoptotic protein with an unclear role in HCC (hepatocellular carcinoma).

RESULTS

In this research, we found that GRAMD4 expression was lower in HCC samples, and its downregulation predicted worse prognosis for patients after surgical resection. Functionally, GRAMD4 inhibited HCC migration, invasion and metastasis. Mechanistically, GRAMD4 interacted with TAK1 to promote its protein degradation, thus, resulting in the inactivation of MAPK (Mitogen-activated protein kinase) and NF-κB pathways. Furthermore, GRAMD4 was proved to recruit ITCH (itchy E3 ubiquitin protein ligase) to promote the ubiquitination of TAK1. Moreover, high expression of TAK1 was correlated with low expression of GRAMD4 in HCC patients.

CONCLUSIONS

GRAMD4 inhibits the migration and metastasis of HCC, mainly by recruiting ITCH to promote the degradation of TAK1, which leads to the inactivation of MAPK and NF-κB signalling pathways.

Stability of a biological tissue fixed with a naturally occurring crosslinking agent (genipin)

The study was undertaken to investigate the stability of a biological tissue fixed with a naturally occurring crosslinking agent (genipin) at distinct elapsed storage durations. The glutaraldehyde-fixed counterpart was used as a control. Porcine pericardia procured from a slaughterhouse were used as raw materials. After fixation, the fixed tissues were sterilized in a graded series of ethanol solutions and thoroughly rinsed in phosphate buffered saline for 1 day, and then stored in a jar containing sterilized water. The samples were taken out and tested for their stability during the durations of 1day through 6 months after storage. The stability of each study group was tested by measuring its tensile strength, free-amino-group content, and denaturation temperature. Additionally, the cytotoxicity of each test sample and its corresponding storage solution were investigated in vitro using 3T3 fibroblasts. The results were examined using a microscope and 3-(4,5-dimethylthiazol-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. It was found that the stability of the genipin-fixed tissue during storage was superior to its glutaraldehyde-fixed counterpart. The differences in stability between the genipin- and glutaraldehyde-fixed tissues during storage may be caused by their differences in crosslinking structure. There was no apparent cytotoxicity for both the genipin-fixed tissue and its corresponding storage solution throughout the entire course of the study, whereas significant cytotoxicity was observed for both the glutaraldehyde-fixed tissue and its storage solution. However, the cytotoxicity of the glutaraldehyde-fixed tissue decreased with increasing elapsed storage duration, whereas that of its corresponding storage solution increased. This suggested that the toxic residues remaining in the glutaraldehyde-fixed tissue leached out slowly into its corresponding storage solution during the course of storage.