A novel Ubc9 -dependent pathway regulates SIRT1- ER-α Axis and BRCA1- associated TNBC lung metastasis

Abstract

Triple negative breast cancer (TNBC) is a heterogeneous disease and has a higher rate of recurrence and distant metastasis. African-American (AA) women have a higher frequency of BRCA1 mutations and TNBC compared to other populations. Basal-like tumors have a higher rate of brain, lung and distant nodal metastasis more than other TNBC subtypes, contributing to higher mortality rate. Our previous work suggested Ubc9, a SUMO E2-conjugating enzyme to induce proliferation and migration of BRCA1-incompetent TNBC cells and TNBC cell lines established from the pleural effusion metastasis of a woman with TNBC. To understand the downstream signaling axis involved in distant metastasis we have used clinically relevant BRCA1 mutant and lung metastatic TNBC cell lines and our results show deregulated expression of caveolin-1, VEGF and SIRT1 in these cells compared to normal mammary epithelial cells by immunofluorescence analysis. We observed SIRT1 to be induced by wild type BRCA1a and BRCA1a I26A mutant unlike the disease associated Ubc9 binding mutants in TNBC cells. Knock down of Ubc9 induced SIRT1 expression in TNBC and ER-α expression in breast cancer cells. This is the first report demonstrating a role for Ubc9 in repressing both SIRT1 and ER-α expression in BRCA1 associated TNBC cells. It also suggests that the BARD-dependent E3 Ubiquitin ligase and HR (homologous recombination) activity of BRCA1 may not be required for inducing SIRT1 expression. Our results suggest for the first time that in BRCA1 mutant TNBC Ubc9-mediated induction of VEGF, inhibition of caveolin-1, SIRT1 and ER-α expression as a novel molecular mechanism underlying TNBC EMT (epithelial mesenchymal transition) leading to lung metastasis with pleural effusion. Drugs that target Ubc9 to both induce SIRT1 and ER-α or using SIRT1 agonists in combination with chemotherapy can be used as a promising targeted therapeutic approach for treating basal-like metastatic BRCA1-linked TNBC thus reducing the mortality in patients with TNBC.

Combined Evaluation of mRNA and Protein Expression, Promoter Methylation, and Immune Infiltration of UBE2I in Pan-Digestive System Tumors

“…Similarly, our results suggest association of high UBC9 expression with poor prognosis in PAAD as well as differential levels (low in normal samples) of promoter methylation concerning lymph node metastasis. The role of UBC9 in PAAD in our study is consistent with that reported in other studies across diverse tumor types, including lung, colorectal, prostate, ovarian, and breast cancers as well as melanoma [ 36 – 41 ]. In addition, we determined the diagnostic potential of UBE2I in PAAD and COAD, which has rarely been reported in cancers.…”

Mutational drivers of cancer cell migration and invasion

“…Mutations in BRCA1 lead to dysregulation of the Ubc9/caveolin-l/vascular endothelial growth factor (VEGF)/SIRTl/oestrogen receptor (ER)-α axis, promote EMT and trigger the migration of HCC1937 triple-negative breast cancer cells in vitro. 58 , 59 The STAG2 gene, the protein product of which regulates centromere cohesion, is often mutated in various cancers. Most STAG2 mutations are truncating and, as shown in the U2OS osteosarcoma cell line, the loss of this gene leads to increased EMT-associated tumour cell migration in vitro, coincident with decreased expression of E-cadherin and increased expression of N-cadherin.…”

A Hypothetical Molecular Mechanism Linking Loss of BRCA1 Function to Infertility

“…In our previous work, we first proposed a novel Ubc9 -Caveolin-1-VEGF-SIRT1-ER-a axis that is facilitated by functional BRCA1 [19]. When BRCA1 is mutated, this axis is disturbed, and it results in TNBC with epithelial to mesenchymal transition that allows for metastasis to the lungs [20]. This mechanism identifies a novel downstream target for BRCA1: SUMO conjugating enzyme Ubc9.…”

“…BRCA1 tethers Ubc9 to prevent Ubc9 tumorpromoting effects. Furthermore, when Ubc9 is bound to BRCA1, SIRT1 expression is activated [20]. Mutant BRCA1 cannot bind Ubc9 leading to accumulation of the enzyme causing reduced expression of Caveolin-1 and increased levels of vascular endothelial growth factor (VEGF), which promotes tumor growth and metastasis.…”