ABSTRACT
Human Mena (hMENA), an actin regulatory protein of the ENA/VASP family, cooperates with ErbB receptor family signaling in breast cancer. It is overexpressed in high-risk preneoplastic lesions and in primary breast tumors where it correlates with HER2 overexpression and an activated status of AKT and MAPK. The concomitant overexpression of hMENA and HER2 in breast cancer patients is indicative of a worse prognosis. hMENA is expressed along with alternatively expressed isoforms, hMENA(11a) and hMENAΔv6 with opposite functions. A novel role for the epithelial-associated hMENA(11a) isoform in sustaining HER3 activation and pro-survival pathways in HER2-overexpressing breast cancer cells has been identified by reverse phase protein array and validated in vivo in a series of breast cancer tissues. As HER3 activation is crucial in mechanisms of cell resistance to PI3K inhibitors, we explored whether hMENA(11a) is involved in these resistance mechanisms. The specific hMENA(11a) depletion switched off the HER3-related pathway activated by PI3K inhibitors and impaired the nuclear accumulation of HER3 transcription factor FOXO3a induced by PI3K inhibitors, whereas PI3K inhibitors activated hMENA(11a) phosphorylation and affected its localization. At the functional level, we found that hMENA(11a) sustains cell proliferation and survival in response to PI3K inhibitor treatment, whereas hMENA(11a) silencing increases molecules involved in cancer cell apoptosis. As shown in three-dimensional cultures, hMENA(11a) contributes to resistance to PI3K inhibition because its depletion drastically reduced cell viability upon treatment with PI3K inhibitor BEZ235. Altogether, these results indicate that hMENA(11a) in HER2-overexpressing breast cancer cells sustains HER3/AKT axis activation and contributes to HER3-mediated resistance mechanisms to PI3K inhibitors. Thus, hMENA(11a) expression can be proposed as a marker of HER3 activation and resistance to PI3K inhibition therapies, to select patients who may benefit from these combined targeted treatments. hMENA(11a) activity could represent a new target for antiproliferative therapies in breast cancer.
Subject(s)
Breast Neoplasms/genetics , Drug Resistance, Neoplasm/genetics , Microfilament Proteins/metabolism , Receptor, ErbB-3/genetics , Antineoplastic Agents/pharmacology , Breast Neoplasms/metabolism , Cell Line, Tumor , Electrophoresis, Gel, Two-Dimensional , Female , Fluorescent Antibody Technique , Humans , Immunohistochemistry , Microfilament Proteins/genetics , Phosphoinositide-3 Kinase Inhibitors , Protein Isoforms , Protein Kinase Inhibitors/pharmacology , RNA, Small Interfering , Real-Time Polymerase Chain Reaction , Receptor, ErbB-2/genetics , TransfectionABSTRACT
Employing purified extracellular matrix (ECM) proteins, i.e. type I, III, IV and V collagens (CI, CIII, CIV, CV), laminin (LM) and fibronectin (FN), as antigen sources we detected autoantibodies to conformational and/or denatured ECM antigens among 34 of 50 sera obtained from Hashimotos thyroiditis (HT) patients and 6 of 51 control sera obtained from non-autoimmune thyroid disease patients and healthy donors (HT sera vs. control sera p=4 x 10-9). Reactivity to conformational antigens, mostly due to autoantibodies of the IgG isotype, was observed in 30/50 HT sera and in 6/51 control sera (p=3.5 x 10-7) and was not always concomitant with that to linear antigens, found in 23/50 HT and in 6/51 control sera (p=1.6 x 10-4). Ultrastructural analysis of skin biopsies obtained from 18 HT patients without symptomatic cutaneous diseases revealed defects of the stratified squamous epithelium basement membrane in 11/18, alterations of the stroma in 13/18 and both basement membrane and stromal defects in 9/18. Interestingly, 13/13 (p=0.012) and 9/11 (p=0.012) patients with stromal and basement membrane defects respectively, exhibited serum antibodies to at least one ECM antigen involved in the organization of the altered tissue compartment. Lastly, 10/18 skin biopsies presented immunoglobulin (Ig) and/or complement (C3) deposits along the cutaneous basement membrane zone (BMZ) or in the papillary dermis and 9/10 sera from the same patients simultaneously showed antibodies to at least one ECM antigen involved in the organization of these two skin compartments. Besides, 8/11 HT patients with basement membrane defects exhibited Ig or C3 deposits along the BMZ. Our findings suggest that autoantibodies to ECM molecules might contribute to the development of asymptomatic extra-thyroid skin diseases in HT patients.
