GRAMD4 regulates PEDV-induced cell apoptosis inhibiting virus replication via the endoplasmic reticulum stress pathway

Porcine epidemic diarrhea (PED) caused by the porcine epidemic diarrhea virus (PEDV) has caused huge losses in the swine industry worldwide. Glucosyltransferase Rab-like GTPase activator and myotubularin domain containing 4 (GRAMD4) is a proapoptotic protein, which replaced p53 inducing mitochondrial apoptosis. However, the relationship between GRAMD4 and PEDV has not been reported. Here, we aimed to investigate the potential role of GRAMD4 during PEDV infection. In this study, we used co-immunoprecipitation (co-IP) and mass spectrometry to identify GRAMD4 interaction with PEDV non-structural protein 6 (NSP6). Immunoprecipitation and laser confocal microscopy were utilized to demonstrate that GRAMD4 interacts with NSP6. NSP6 reduces GRAMD4 production through PERK and IRE1 pathway-mediated apoptosis. We demonstrated that overexpression of GRAMD4 effectively impaired the replication of PEDV, whereas knockdown of GRAMD4 facilitated the replication of PEDV. Overexpression of GRAMD4 increased GRP78, phosphorylated PERK (p-PERK), phosphorylated IRE1(p-IRE1) levels, promoted CHOP, phosphorylated JNK (p-JNK), Bax expression, caspase 9 and caspase 3 cleavage, and inhibited Bcl-2 production. Knockdown of GRAMD4 has the opposite effect. Finally, deletion of the GRAM domain of GRAMD4 cannot cause endoplasmic reticulum stress (ER stress)-mediated apoptosis and inhibit virus replication. In conclusion, these studies revealed the mechanism by which GRAMD4 was associated with ER stress and apoptosis regulating PEDV replication. NSP6 acted as a potential down-regulator of GRAMD4 and promoted the degradation of GRAMD4. GRAMD4 played a role in facilitating apoptosis and restricting virus replication, and the GRAM domain was required. These findings provided a reference for host-PEDV interactions and offered the possibility for PEDV decontamination and prevention.

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.