Serglycin Cooperates with the Unfolded Protein Response Pathway and Inflammation to Drive Glioblastoma Cell Survival

Serglycin (SRGN) has been found overexpressed and secreted in glioblastoma (GBM), associated with tumorigenic signaling and poor prognosis. In this study, we aimed to elucidate the involvement of SRGN in the unfolded protein response (UPR), an oncogenic signaling pathway implicated in protein recycling and cell fate. Herein, we developed stably transduced LN-18^shSCR GBM cells, expressing high levels of SRGN, and SRGN-depleted LN-18^shSRGN cells. We observed significantly attenuated expression and activity of all UPR mediators upon SRGN suppression, in particular PERK, IRE1, ATF6 and downstream effectors. SRGN-expressing cells possessed a constitutively active UPR, as indicated by its active phosphorylation status and accumulated pool of nuclear ATF4 in LN-18^shSCR cells. Constitutive activation of the caspase-dependent apoptotic pathway was apparent in LN-18^shSRGN cells. Induction of endoplasmic reticulum (ER) stress pointed out that LN-18^shSRGN cells were predisposed to ER stress-associated cell death, whereas LN-18^shSCR cells activated adaptive UPR signaling and displayed resistance to apoptosis. The evaluation of TLRs, TNFRs, ILs and NF-kB also underscored that SRGN is essential for their expression and active inflammatory signaling. We concluded that SRGN-expressing cells acquire a pro-survival UPR mechanism, highlighting the novel regulatory role of SRGN in the adaptation and survival of GBM cells.