The Human Minor Histocompatibility Antigen1 Is a RhoGAP

Abstract

The human minor Histocompatibility Antigen HMHA-1 is a major target of immune responses after allogeneic stem cell transplantation applied for the treatment of leukemia and solid tumors. The restriction of its expression to hematopoietic cells and many solid tumors raised questions regarding its cellular functions. Sequence analysis of the HMHA-1 encoding HMHA1 protein revealed the presence of a possible C-terminal RhoGTPase Activating Protein (GAP) domain and an N-terminal BAR domain. Rho-family GTPases, including Rac1, Cdc42, and RhoA are key regulators of the actin cytoskeleton and control cell spreading and migration. RhoGTPase activity is under tight control as aberrant signaling can lead to pathology, including inflammation and cancer. Whereas Guanine nucleotide Exchange Factors (GEFs) mediate the exchange of GDP for GTP resulting in RhoGTPase activation, GAPs catalyze the low intrinsic GTPase activity of active RhoGTPases, resulting in inactivation. Here we identify the HMHA1 protein as a novel RhoGAP. We show that HMHA1 constructs, lacking the N-terminal region, negatively regulate the actin cytoskeleton as well as cell spreading. Furthermore, we show that HMHA1 regulates RhoGTPase activity in vitro and in vivo. Finally, we demonstrate that the HMHA1 N-terminal BAR domain is auto-inhibitory as HMHA1 mutants lacking this region, but not full-length HMHA1, showed GAP activity towards RhoGTPases. In conclusion, this study shows that HMHA1 acts as a RhoGAP to regulate GTPase activity, cytoskeletal remodeling and cell spreading, which are crucial functions in normal hematopoietic and cancer cells.

Yeast Translation Elongation Factor-1A Binds Vacuole-localized Rho1p to Facilitate Membrane Integrity through F-actin Remodeling

“…We deemed that eEF1A is most likely a downstream effector of Rho1p because its protein sequence does not contain domains typical for GEFs and GAPs such as Dbl homology-pleckstrin homology domains for Rho GEFs (33) and BH domains for Rho GAPs (34,35). Rho effectors preferentially bind to Rho proteins in the GTP-bound state (36 -38).…”

Tumor Evolution Decoder (TED): Unveiling Tumor Evolution Based on Mutation Profiles of Subclones or Single Cells

“…GSEA shows that RhoA regulation related pathways that regulate cell shape, attachment, and motility are statistically significantly enriched in the CDS-SNV genes on the normal → subclone 4 edge, including DLC1, an important gene in the RhoA regulation related pathways that has been reported with the potential of suppressing breast cancer bone metastasis and whose mutation may lead to metastasis 39 . The RhoA regulation related pathways are also significantly enriched in the CDS-CNA genes on the edge of subclone 4 → subclone 2, including ARHGAP45 (Rho GTPase activating protein 45) that has been reported to act as a RhoGAP to regulate GTPase activity, cytoskeletal remodeling and cell spreading 40 . The copy number of ARHGAP45 is amplified in this evolution step, leading to more metastasis potential of subclone 2.…”

Phosphoproteomic analysis of kinase-deficient mice reveals multiple TAK1 targets in osteoclast differentiation

“…Modulators of small GTPase signaling, such as guanine nucleotide exchange factors (GEFs), GTPase-activating proteins (GAPs) and GTPase effectors were TAK1-dependently phosphorylated (Table 1 and Supplemental Table S1): Arhgef12/LARG, a RhoGEF, and Psd4/ EFA6B, an Arf6GEF, have roles in cell polarization in neurons and epithelial cells [29e31]. Hmha1, a RhoGAP, and Usp6nl/RN-Tre, a RabGAP, have roles in membrane trafficking [32,33]. Rabep1/ Rabaptin-5 functions as a Rab GTPase effector in fibroblasts and epithelial cells [34].…”