Proteomic profiling of the oncogenic septin 9 reveals isoform‐specific interactions in breast cancer cells

Abstract

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.

Epigenetic Regulation Explains The Functionality Behind Colon Cancer Specific Biomarker Septin9

“…The expression of Septin9 has been shown to have both tumor suppressor and promoting effects in other cancers, but its complete absence can be lethal to cells [16,[23][24][25][26][27][28][29]. Hypermethylation of a specific region of the Septin9 gene at the v2 promoter region is a well-known early event in CRC formation [5].…”

“…In about 20% of breast cancer cases amplification of the Septin9 gene occurs in double-minute chromosomes, leading to overexpression related to a higher invasion and migration ability of tumor cells [26][27][28]. Moreover, isoform-specific differences were also shown in interactions with proteins of distinct subcellular organelles and functions [29]. The truncated isoforms 4 and 5 interacting with any member of Septin6 group play a role in cellular signaling and protein ubiquitination, whereas isoform 1 mainly interacts with only Septin8 and regulates cytoskeleton rearrangements.…”

Septins as membrane influencers: direct play or in association with other cytoskeleton partners

“…At last, intermediate filaments (IFs) have also been identified as binding partners of oncogenic SEPT9 isoforms by proteomic profiling (Devlin et al, 2021). During human spermiogenesis, SEPT12 is recovered in a complex with the IF nucleo-cytoskeleton laminB1 and the nuclear membrane cytoskeleton-linker protein SUN4/SPAG4 during the formation of nuclear envelopes of round spermatids (Yeh et al, 2015).…”

ISGylation of EMD promotes its interaction with PDHA to inhibit aerobic oxidation in lung adenocarcinoma

“…4 Alterations in cytoskeletal proteins also lead to nuclear abnormalities common in a wide range of cancer types. 5 It has long been recognized that tumour cells frequently exhibit abnormal nuclear architecture, including nuclear size and structure, nucleolar size and number and chromatin texture, and that these alterations are critical risk factors for tumour formation and developments. 6,7 Emerin (EMD) is 254 amino acids in length and with an N-terminal globular LAP2-EMD-MAN1 (LEM, aa: 1-45) domain, followed by an βcatenin interaction (IT, aa: 168-186) domain, 8 and anchored to the nuclear envelope.…”