Bcl-2-associated transcription factor 1 Ser290 phosphorylation mediates DNA damage response and regulates radiosensitivity in gastric cancer

Abstract

Background DNA damage response plays critical roles in tumor pathogenesis and radiotherapy resistance. Protein phosphorylation is a critical mechanism in regulation of DNA damage response; however, the key mediators for radiosensitivity in gastric cancer still needs further exploration. Methods A quick label-free phosphoproteomics using high-resolution mass spectrometry and an open search approach was applied to paired tumor and adjacent tissues from five patients with gastric cancer. The dysregulated phosphoproteins were identified and their associated-pathways analyzed using Gene Set Enrichment Analysis (GSEA). The mostly regulated phosphoproteins and their potential functions were validated by the specific antibodies against the phosphorylation sites. Specific protein phosphorylation was further analyzed by functional and clinical approaches. Results 832 gastric cancer-associated unique phosphorylated sites were identified, among which 25 were up- and 52 down-regulated. Markedly, the dysregulated phosphoproteins were primarily enriched in DNA-damage-response-associated pathways. Particularly, the phosphorylation of Bcl-2-associated transcription factor 1 (BCLAF1) at Ser290 was significantly upregulated in tumor. The upregulation of BCLAF1 Ser290 phosphorylation (pBCLAF1 (Ser290)) in tumor was confirmed by tissue microarray studies and further indicated in association with poor prognosis of gastric cancer patients. Eliminating the phosphorylation of BCLAF1 at Ser290 suppressed gastric cancer (GC) cell proliferation. Upregulation of pBCLAF1 (Ser290) was found in association with irradiation-induced γ-H2AX expression in the nucleus, leading to an increased DNA damage repair response, and a marked inhibition of irradiation-induced cancer cell apoptosis. Conclusions The phosphorylation of BCLAF1 at Ser290 is involved in the regulation of DNA damage response, indicating an important target for the resistance of radiotherapy.

Function of BCLAF1 in human disease (Review)

“…Similarly, in the latest research, IR induced phosphorylation of serine 290 in BCLAF1 and the co-localization of BCLAF1 with γH2AX, which promoted DDR and radiotherapy resistance of gastric cancer cells ( Fig. 1B-i ) ( 11 ). In addition, Savage et al ( 3 ) discovered that BCLAF1 was identified in the protein interacting with BRCA1, which mediated the formation of the BRCA1-mRNA splice complex after DNA damage, and knockdown of BCLAF1 increased cell sensitivity to IR.…”

“…1A and B-a ). Similarly, a recent study proved that the phosphorylation of BCLAF1 at serine 290 participated in DDR mediated by H2AX phosphorylated on serine 139 (γH2AX) ( 11 ). Lastly, heat shock protein 90α (Hsp90α) was found to bind to BCLAF1 and stabilize its protein structure, thus preventing BCLAF1 from degradation via the ubiquitin-proteasome system (UPS) in HCC ( Fig.…”

“…Collectively, another three studies also confirmed that BCLAF1 acted as a tumor suppressor in lung cancer (LC), multiple myeloma (MM) and DLBCL ( 7 , 21 , 35 ). However, recently, BCLAF1 has become a hot topic due to its carcinogenic characteristics in certain types of human cancer, including colorectal cancer (CRC) ( 34 ), BC ( 22 , 36 ), AML ( 38 ), LC ( 40 ), HCC ( 30 , 31 , 37 , 39 , 42 ) and gastric cancer ( 11 ). These differences indicated that the specific role of BCLAF1 in tumor progression may depend on the cellular context and type of cancer ( Table IV ).…”

“…BCLAF1 was originally identified as a binding protein that interacted with adenoviral Bcl-2 homolog E1B19K, and served as an inducer of apoptosis and suppressor of transcription ( 1 ). Subsequent studies have shown that BCLAF1 also played a key role in a wide range of biological processes, including pre-mRNA splicing and processing ( 2 – 6 ), DNA damage response (DDR) ( 3 , 4 , 7 – 11 ), lung development ( 12 ), viral infection ( 13 – 16 ), muscle cell proliferation and differentiation ( 17 – 20 ), autophagy ( 21 , 22 ), ischemia-reperfusion (I/R) injury ( 23 ), and T-cell activation ( 12 , 24 , 25 ).…”

“…1B-a ) ( 7 ). Notably, increasing evidence has demonstrated that BCLAF1 was associated with tumorigenesis as either a tumor promotor ( 11 , 22 , 30 , 31 , 34 , 37 – 42 ) or a tumor suppressor ( 7 , 21 , 32 , 35 , 43 ) in a context-dependent manner. In addition to for tumorigenesis and viral replication, BCLAF1 has also been associated with cardiac I/R injury ( 23 ).…”