Septins are a family of multimeric GTP-binding proteins, which are abnormally expressed in cancer. Septin 9 (SEPT9) is an essential and ubiquitously expressed septin with multiple isoforms, which have differential expression patterns and effects in breast cancer cells. It is unknown, however, if SEPT9 isoforms associate with different molecular networks and functions. Here, we performed a proteomic screen in MCF-7 breast cancer cells to identify the interactome of GFP-SEPT9 isoforms 1, 4 and 5, which vary significantly in their N-terminal extensions. While all three isoforms associated with SEPT2 and SEPT7, the truncated SEPT9_i4 and SEPT9_i5 interacted with septins of the SEPT6 group more promiscuously than SEPT9_i1, which bound predominately SEPT8. Spatial mapping and functional clustering of non-septin partners showed isoform-specific differences in interactions with proteins of distinct subcellular organelles (e.g., nuclei, centrosomes, cilia) and functions such as cell signalling and ubiquitination. The interactome of the full length SEPT9_i1 was more enriched in cytoskeletal regulators, while the truncated SEPT9_i4 and SEPT9_i5 exhibited preferential and isoform-specific interactions with nuclear, signalling, and ubiquitinating proteins. These data provide evidence for isoform-specific interactions, which arise from truncations in the N-terminal extensions of SEPT9, and point to novel roles in the pathogenesis of breast cancer.
Septins are a family of multimeric GTP-binding proteins, which are abnormally expressed in cancer. Septin 9 (SEPT9) is an essential and ubiquitously expressed septin with multiple isoforms, which have differential expression patterns and effects in breast cancer cells. It is unknown, however, if SEPT9 isoforms associate with different molecular networks and functions. Here, we performed a proteomic screen in MCF-7 breast cancer cells to identify the interactome of GFP-SEPT9 isoforms 1, 4 and 5, which vary significantly in their N-terminal extensions. While all three isoforms associated with SEPT2 and SEPT7, the truncated SEPT9_i4 and SEPT9_i5 interacted with septins of the SEPT6 group more promiscuously than SEPT9_i1, which bound predominately SEPT8. Spatial mapping and functional clustering of non-septin partners showed isoform-specific differences in interactions with proteins of distinct subcellular organelles (e.g., nuclei, centrosomes, cilia) and functions such as cell signaling and ubiquitination. Notably, the interactome of the full length SEPT9_i1 was more enriched in cytoskeletal regulators, while the truncated SEPT9_i4 and SEPT9_i5 exhibited preferential and isoform-specific interactions with nuclear, signaling and ubiquitinating proteins. These data provide evidence for isoform-specific interactions, which arise from truncations in the N-terminal extensions of SEPT9, and point to novel roles in the pathogenesis of breast cancer. L.D. performed experiments, analyzed data, made figures and co-wrote manuscript with E.T.S.; G.P. contributed technically and intellectually to ESI/LC-MS/MS experimentation and softwarebased peptide identification; J.R.B. performed microscopy imaging; C.M. created MCF-7 cell lines and contributed to the manuscript; E.T.S. conceived and directed the project (experiments and analyses), drafted manuscript and edited figures.
We previously reported the safety and immunogenicity data from a randomized trial comparing the monovalent (MV) recombinant protein Beta-variant (MVB.1.351) and MV ancestral protein (MVD614) booster vaccines with AS03 adjuvant (Sanofi/GSK) to mRNA BNT162b2 vaccine (Pfizer-BioNTech). First booster of the vaccines was administered in adult participants previously primed with 2 doses of BNT162b2. A subset of these participants with available blood samples collected at Day 0 (D0), at 28 days (D28), and 3 months (M3) post-booster were contacted for additional testing (195/208 participants). The persistence of cross-neutralizing antibodies, including against Omicron BA.1 and BA.4/5, up to 3 months after boosting was evaluated using a validated pseudovirus neutralization assay. The data showed that the MVB.1.351 vaccine induced higher and durable cross-neutralizing antibodies against Omicron subvariants up to 3 months after boosting compared to a MV ancestral and the mRNA BNT162b2 booster vaccine.
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