Novel CTRP8-RXFP1-JAK3-STAT3 axis promotes Cdc42-dependent actin remodeling for enhanced filopodia formation and motility in human glioblastoma cells.

Abstract

CTRP8 is the least studied member of the C1Q-TNF related peptide family. We identified CTRP8 as a ligand of the G protein coupled receptor RXFP1 in glioblastoma multiforme (GBM). The CTRP8-RXFP1 ligand-receptor system protects human GBM cells against the DNA alkylating damage inducing temozolomide (TMZ), the drug of choice for the treatment of patients with GBM. The DNA protective role of CTRP8 was dependent on a functional RXFP1-STAT3 signaling cascade and targeted the mono-functional glycosylase N-methylpurine DNA glycosylase (MPG) for more efficient base excision repair of TMZ induced DNA damaged sites. CTRP8 also improved survival of GBM cells by up-regulating anti-apoptotic BCl-2 and BCL-XL. Here, we have identified JAK3 as a novel member of a novel CTRP8-RXFP1-JAK3-STAT3 signaling cascade that caused an increase in cellular protein content and activity of the small Rho GTPase Cdc42. This is associated with significant F-actin remodeling and increased GBM motility. Cdc42 was critically important for the upregulation of the actin nucleation complex N-WASP/Arp3/4 and actin elongation factor profilin-1. Activation of the RXFP1-JAK3-STAT3-Cdc42 axis by both RXFP1 agonists, CTRP8 and RLN2, caused extensive filopodia formation. This coincided with enhanced activity of ezrin, a key factor in tethering F-actin to the plasma membrane, and inhibition of the actin filament severing activity of cofilin. The Cdc42 mediated F-actin remodeling and pro-migratory action of the novel RXFP1-JAK3-STAT3-Cdc42 axis was blocked by JAK3 inhibitor Tofacitinib and STAT3 inhibitor S3I-201 and provides a new rationale for the design of JAK3 and STAT3 inhibitors with better brain permeability for clinical treatment of the pervasive brain invasiveness of GBM.