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 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.

The Prognostic Biomarkers and Immunotherapeutic Targets of Septin in Colon Cancer

“…Recent studies revealed that SEPT6 was the upstream gene of UBC in prostate cancer and inhibited tumor growth by regulating UBC [33]. Other evidences showed that SEPT6 was also participated in the pathogenesis of breast cancer and hepatocellular carcinoma, which suggested that targeting SEPT6 may be a new therapeutic strategy for cancers [34,35]. Overexpression of SEPT7 plays a crux role in inhibiting the growth and migration of glioma cells [36,37].…”

Potential of blood exosomal ENAH, SEPT9, EGF, MMP‑9 and CXCL8 for the early screening of breast cancer

“…For instance, previous studies showed that enabled homolog (ENAH), an actin regulatory protein of the enabled/vasodilator-stimulated phosphoprotein family, promoted the proliferation, invasion and epithelial-mesenchymal transition of breast cancer cells when overexpressed (12,13). Also, other studies showed that septin 9 (SEPT9), an oncogenic protein, was dysregulated in patients with breast cancer with lymph node metastases and regulated the migration of breast cancer cells via ras homolog family member A/focal adhesion kinase signaling (14,15). Additionally, epidermal growth factor (EGF) has been reported to interact with its receptor to regulate the carcinogenesis and malignant behavior of breast cancer cells (16,17).…”

Spatial regulation of microtubule-dependent transport by septin GTPases

“…Because centrosomal levels of SEPT7 decrease during mitosis, and SEPT7 depletion impacts on entry into S phase [57], SEPT7 appears to function in centrosome duplication before mitosis. Although the precise role of SEPT7 is unknown, p150 GLUED localizes to the subdistal appendages of the mother centriole which anchor microtubule minusends, and impacts on the recruitment of the subdistal appendage proteins ninein and CEP170 which interact with SEPT9 and SEPT1, respectively [79][80][81]. Of note, SEPT1 is also enriched in spindle poles [82].…”