Non-apoptotic activity of the mitochondrial protein SMAC/Diablo in lung cancer: Novel target to disrupt survival, inflammation, and immunosuppression

Abstract

Mitochondrial SMAC/Diablo induces apoptosis by binding the inhibitor of apoptosis proteins (IAPs), thereby activating caspases and, subsequently, apoptosis. Previously, we found that despite its pro-apoptotic activity, SMAC/Diablo is overexpressed in cancer, and demonstrated that in cancer it possesses new essential and non-apoptotic functions that are associated with regulating phospholipid synthesis including modulating mitochondrial phosphatidylserine decarboxylase activity. Here, we demonstrate additional functions for SMAC/Diablo associated with inflammation and immunity. CRISPR/Cas9 SMAC/Diablo-depleted A549 lung cancer cells displayed inhibited cell proliferation and migration. Proteomics analysis of these cells revealed altered expression of proteins associated with lipids synthesis and signaling, vesicular transport and trafficking, metabolism, epigenetics, the extracellular matrix, cell signaling, and neutrophil-mediated immunity. SMAC-KO A549 cell-showed inhibited tumor growth and proliferation and activated apoptosis. The small SMAC-depleted “tumor” showed a morphology of alveoli-like structures, reversed epithelial-mesenchymal transition, and altered tumor microenvironment. The SMAC-lacking tumor showed reduced expression of inflammation-related proteins such as NF-kB and TNF-α, and of the PD-L1, associated with immune system suppression. These results suggest that SMAC is involved in multiple processes that are essential for tumor growth and progression. Thus, targeting SMAC’s non-canonical function is a potential strategy to treat cancer.

Apoptotic proteins with non-apoptotic activity: expression and function in cancer

“…In the ER, PS is produced from PC and PE by PSS1 and PSS2, respectively, and then transferred to the mitochondria, where it is converted into PE by PSD [ 250 ]. (III) Inhibition or modulation of inflammation and immunity in the small tumors developed from CRISPER/Cas9 SMAC/Diablo-depleted A549 lung cancer cells showed reduced expression of inflammation-related proteins such as NF-kB and TNF-α and of the programmed death-ligand 1 PD-L1 associated with additive immune system suppression [ 13 ] …”

“…The si-hSMAC-treated residual tumor demonstrated morphological changes, including cell differentiation and reorganization into glandular/alveoli-like structures and elimination of surfactant-producing organs, the lamellar bodies [ 12 , 14 ]. Similarly, CRISPER/Cas9 SMAC/Diablo-depleted A549 lung cancer cells displayed inhibited cell proliferation and cell migration [ 13 ]. Using the proteomic approach of LC–MS/MS analysis, these SMAC/Diablo depleted cells, showed altered expression of proteins associated with lipid- and lipid signaling, vesicular transport and trafficking, metabolism, epigenetic, extracellular matrix, cell signaling and neutrophil-mediated immunity [ 13 ].…”

“…Similarly, CRISPER/Cas9 SMAC/Diablo-depleted A549 lung cancer cells displayed inhibited cell proliferation and cell migration [ 13 ]. Using the proteomic approach of LC–MS/MS analysis, these SMAC/Diablo depleted cells, showed altered expression of proteins associated with lipid- and lipid signaling, vesicular transport and trafficking, metabolism, epigenetic, extracellular matrix, cell signaling and neutrophil-mediated immunity [ 13 ].…”

“…Moreover, tumors established from SMAC-KO A549 cells showed, altered expression of several components of the tumor microenvironment, reduced expression of inflammation-related proteins such as NF-kB and TNF-α and of the programmed death-ligand 1 PD-L1 associated with additive immune system suppression [ 13 ].…”

Isorhamnetin Regulates Programmed Death Ligand-1 Expression by Suppressing the EGFR–STAT3 Signaling Pathway in Canine Mammary Tumors

“…Research into PD-L1 is a hot topic in oncology, particularly for the treatment of breast cancer [ 11 ]. Inhibition of different types of lung cancer cells by preventing PD-L1 expression can be achieved by reducing the mitochondrial membrane potential to induce apoptosis in these cells [ 12 ]. In addition to lung cancer cells, PD-L1 also shows higher expression on the surface of some types of breast cancer cells, providing a possible potential treatment target.…”