Comparison of the MAID (AI) and CAV/IE regimens with the predictive value of cyclic AMP-responsive element-binding protein 3 like protein 1 (CREB3L1) in palliative chemotherapy for advanced soft-tissue sarcoma patients

The Regulatory Network of CREB3L1 and Its Roles in Physiological and Pathological Conditions

CREB3 subfamily belongs to the bZIP transcription factor family and comprises five members. Normally they are located on the endoplasmic reticulum (ER) membranes and proteolytically activated through RIP (regulated intramembrane proteolysis) on Golgi apparatus to liberate the N-terminus to serve as transcription factors. CREB3L1 acting as one of them transcriptionally regulates the expressions of target genes and exhibits distinct functions from the other members of CREB3 family in eukaryotes. Physiologically, CREB3L1 involves in the regulation of bone morphogenesis, neurogenesis, neuroendocrine, secretory cell differentiation, and angiogenesis. Pathologically, CREB3L1 implicates in the modulation of osteogenesis imperfecta, low grade fibro myxoid sarcoma (LGFMS), sclerosing epithelioid fibrosarcoma (SEF), glioma, breast cancer, thyroid cancer, and tissue fibrosis. This review summarizes the upstream and downstream regulatory network of CREB3L1 and thoroughly presents our current understanding of CREB3L1 research progress in both physiological and pathological conditions with special focus on the novel findings of CREB3L1 in cancers.

Induction of cell death in ovarian cancer cells by doxorubicin and oncolytic vaccinia virus is associated with CREB3L1 activation

We have demonstrated that oncolytic vaccinia virus synergizes with doxorubicin (DOX) in inducing immunogenic cell death in platinum-resistant ovarian cancer cells and increases survival in syngeneic and xenograft tumor models. However, the mechanisms underlying the virus- and doxorubicin-mediated cancer cell death remain unknown. In this study, we investigated the effect of the oncolytic virus and doxorubicin used alone or in combination on activation of the cytoplasmic transcription factor CREB3L1 (cyclic AMP [cAMP] response element-binding protein 3-like 1) in ovarian cancer cell lines and clinical specimens. We demonstrated that doxorubicin-mediated cell death in ovarian cancer cell lines was associated with nuclear translocation of CREB3L1 and that the effect was augmented by infection with oncolytic vaccinia virus or treatment with recombinant interferon (IFN)-β used as a viral surrogate. This combination treatment was also effective in mediating nuclear translocation of CREB3L1 in cancer cells isolated from ovarian tumor biopsies at different stages of disease progression. The measurement of CREB3L1 expression in clinical specimens of ovarian cancer revealed lack of correlation with the stage of disease progression, suggesting that understanding the mechanisms of nuclear accumulation of CREB3L1 after doxorubicin treatment alone or in combination with oncolytic virotherapy may lead to the development of more effective treatment strategies against ovarian cancer.

Regulated Alternative Translocation: A Mechanism Regulating Transmembrane Proteins Through Topological Inversion

Transmembrane proteins must adopt a proper topology to execute their functions. In mammalian cells, a transmembrane protein is believed to adopt a fixed topology. This assumption has been challenged by recent reports that ceramide or related sphingolipids regulate some transmembrane proteins by inverting their topology. Ceramide inverts the topology of certain newly synthesized polytopic transmembrane proteins by altering the direction through which their first transmembrane helices are translocated across membranes. Thus, this regulatory mechanism has been designated as Regulated Alternative Translocation (RAT). The physiological importance of this topological regulation has been demonstrated by the finding that ceramide-induced RAT of TM4SF20 (Transmembrane 4 L6 family member 20) is crucial for the effectiveness of doxorubicin-based chemotherapy, and that dihydroceramide-induced RAT of CCR5 (C-C chemokine receptor type 5), a G protein-coupled receptor, is required for lipopolysaccharide (LPS) to inhibit chemotaxis of macrophages. These observations suggest that topological inversion through RAT could be an emerging mechanism to regulate transmembrane proteins.

Transcription factors activated through RIP (regulated intramembrane proteolysis) and RAT (regulated alternative translocation)

Transmembrane proteins are membrane-anchored proteins whose topologies are important for their functions. These properties enable regulation of certain transmembrane proteins by regulated intramembrane proteolysis (RIP) and regulated alternative translocation (RAT). RIP enables a protein fragment of a transmembrane precursor to function at a new location, and RAT leads to an inverted topology of a transmembrane protein by altering the direction of its translocation across membranes during translation. RIP mediated by site-1 protease (S1P) and site-2 protease (S2P) is involved in proteolytic activation of membrane-bound transcription factors. In resting cells, these transcription factors remain in the endoplasmic reticulum (ER) as inactive transmembrane precursors. Upon stimulation by signals within the ER, they are translocated from the ER to the Golgi. There, they are cleaved first by S1P and then by S2P, liberating their N-terminal domains from membranes and enabling them to activate genes in the nucleus. This signaling pathway regulates lipid metabolism, unfolded protein responses, secretion of extracellular matrix proteins, and cell proliferation. Remarkably, ceramide-induced RIP of cAMP response element-binding protein 3-like 1 (CREB3L1) also involves RAT. In resting cells, RIP of CREB3L1 is blocked by transmembrane 4 L6 family member 20 (TM4SF20). Ceramide inverts the orientation of newly synthesized TM4SF20 in membranes through RAT, converting TM4SF20 from an inhibitor to an activator of RIP of CREB3L1. Here, I review recent insights into RIP of membrane-bound transcription factors, focusing on CREB3L1 activation through both RIP and RAT, and discuss current open questions about these two signaling pathways.