Rac1 GTPase is activated by hepatitis B virus replication — involvement of HBX

Abstract

Hepatitis B virus (HBV) is a causative agent for liver diseases including hepatocellular carcinoma. Understanding its interactions with cellular proteins is critical in the elucidation of the mechanisms of disease progression. Using a cell-based HBV replication system, we showed that HBV replication in HepG2 cells resulted in a cellular morphological changes displaying membrane rufflings and lamellipodia like structures reminiscent of cells expressing constitutively activated Rac1. We also showed that activated Rac1 resulted in increased viral replication. HBV replication specifically activated wild type Rac1, but not Cdc42. The Rac1 activation by HBV replication also resulted in the phosphorylation of ERK1/2 and AKT, the downstream targets of Rac1 signaling cascade. The smallest HBV viral protein, HBX, was able to activate the endogenous Rac1 and induce membrane ruffling when transfected into cells. Significantly, HBX was found to directly interact with a Rac1 nucleotide exchange factor (betaPIX) through a SH3 binding motif. Taken together, we have shown the interaction of HBV with the Rho GTPase, affecting cell morphology through the Rac1 activation pathway. HBV may possibly make use of an activated Rac1 signaling pathway for increased replication and resultant metastatic effects.

Small Rho GTPases and Cholesterol Biosynthetic Pathway Intermediates in African Swine Fever Virus Infection

“…RhoA signaling is required for respiratory syncytial virus replication and morphogenesis (26). Moreover, the expression of active Rac1 is increased after hepatitis B virus replication (59).…”

The regulation of proteins associated with the cytoskeleton by hepatitis B virus X protein during hepatocarcinogenesis

“…Previous studies have demonstrated that HBV infection is able to induce CPEs in hepatocytes, with a ground glass appearance in the human liver/promoter-driven urokinase-type plasminogen activator/severe combined immunodeficiency mouse model or in cultured HeLa cells (19,20). Further studies reported that HBV-replicating HepG2 cells exhibited morphological changes and had the appearance of membrane rufflings and lamellipodia-like structures (21). The proteins belonging to the Rho GTPase family function as molecular switches and cycle from a GDP-bound inactive form to a GTP-bound active form (22).…”

“…The proteins belonging to the Rho GTPase family function as molecular switches and cycle from a GDP-bound inactive form to a GTP-bound active form (22). These proteins include ATP-dependent RNA helicase A, Ras-related C3 botulinum (Rac) and cell division control protein 42 (Cdc42), which are implicated in regulating the assembly and organization of the cytoskeleton and are involved in cell morphogenesis (21,22). Through implementing a cell-based HBV replication system, the shape change of cells infected with this virus has been proposed to be associated with the constitutively activated Rac substrate 1 (Rac1) (21).…”

“…Through implementing a cell-based HBV replication system, the shape change of cells infected with this virus has been proposed to be associated with the constitutively activated Rac substrate 1 (Rac1) (21). Notably, the interaction of Rac1 nucleotide exchange factor (βPIX) with HBx via an SRC homology 3 (SH3) domain-binding motif controlled the activation of endogenous Rac1 to induce membrane ruffling during HBV infection (21). In addition, HBx expressing HepG2 cells have been observed with long pseudopods (23).…”

“…These proteins include ATP-dependent RNA helicase A, Ras-related C3 botulinum (Rac) and cell division control protein 42 (Cdc42), which are implicated in regulating the assembly and organization of the cytoskeleton and are involved in cell morphogenesis (21,22). Through implementing a cell-based HBV replication system, the shape change of cells infected with this virus has been proposed to be associated with the constitutively activated Rac substrate 1 (Rac1) (21). Notably, the interaction of Rac1 nucleotide exchange factor (βPIX) with HBx via an SRC homology 3 (SH3) domain-binding motif controlled the activation of endogenous Rac1 to induce membrane ruffling during HBV infection (21).…”