RhoH plays distinct roles in T-cell migrations induced by different doses of SDF1α

Hematopoietic-specific RhoGTPase RhoH displays an important role in regulating T-cell development, a process that is accompanied by ordered and directed migration of progenitors through thymus. While RhoGTPases are key regulators of cytokinesis, the precise role of RhoH in T-cell migration is unknown. Here, by using Jurkat cell migration as a model, we found that RhoH is required for cell migration in response to the high concentration of SDF1α but displays inhibitory roles in regulating migration in the absence of SDF1α or in the range of low concentrations. We further found that RhoH-mediated migration requires PAK1 but not ITK. Indeed, both the low and high concentrations of SDF1α activate PAK1 but only the high concentration-induced activation of PAK1 requires RhoH. Further study of the RhoH-PAK interaction revealed that RhoH is able to bind and activate PAK1, indicating that RhoH plays a positive role in response to the high concentration of SDF1α. In contrast, at rest, RhoH indirectly inhibits Slp76/ITK activity through its modulation on TCR signaling, supporting a negative regulatory role for RhoH when SDF1α is insufficient to activate the RhoH-PAK1 pathway. Together, our study uncovered a dual role for RhoH in SDF1α signaling in T-cell responses.