Dysregulated connexin 43 in HER2-positive drug resistant breast cancer cells enhances proliferation and migration

Abstract

Connexin 43 (Cx43) is a gap junction protein whose function in the development of breast cancer and in breast cancer progression remains unclear. Evidence suggests that Cx43 (GJA1) mRNA and protein expression is altered in breast tumors. However, reports indicate both increased and decreased Cx43 levels in human breast cancer samples. Studies also suggest that loss of Cx43 regulated gap junction intercellular communication is a common feature of breast malignancies that potentially correlates with histological stage. Further evidence suggests that Cx43 (GJA1) mRNA expression is negatively correlated with HER2 positivity but a relationship between Cx43 and HER2 in breast cancer is not well defined. Therefore, in this study, we sought to evaluate the relationship between Cx43 activity, HER2, and drug resistance. Using HER2+ breast cancer cell lines that are sensitive or resistant to HER2 inhibitor, we evaluated Cx43 gap junction function. We found that Cx43 gap junction activity is completely lost in drug resistant HER2-positive (HER2+) breast cancer cells, whereas Cx43 gap junction activity can be restored by Cx43 overexpression in drug sensitive HER2+ cells. Moreover, the dysregulation of Cx43 resulted in increased tumorigenic and migratory capacity of the HER2+ drug resistant breast cancer cells.

The Complex Subtype-Dependent Role of Connexin 43 (GJA1) in Breast Cancer

“…A previous study using immunohistochemistry found no correlation between Cx43 protein level and patient outcome [ 44 ]. However, similar to our results, more recent studies using expression array-based survival curves found that a high GJA1 expression was associated with a better prognosis in ER -positive breast cancer tumors, while an opposite trend was observed in ER -negative tumors [ 33 ] and Her2e tumors [ 34 ]. The worse prognosis associated with GJA1 in Her2e tumors suggests that GJA1 function in breast cancer might not just be tissue- and stage-dependent, as suggested by others [ 11 , 17 ], but might also be subtype-dependent.…”

“…To gain further insight into the role of Cx43 in breast cancer, we analyzed how the level of GJA1 mRNA expression in each subtype was associated with outcome. Observations that Cx43 expression was associated with a worse prognostic in ER-negative [ 33 ] and Her2e [ 34 ] tumors have been previously reported using the web-based platform KMPlotter [ 35 ] while ER-positive tumors had a better prognosis [ 33 ]. Investigating further the results of BreastMark and KMPlotter Web platforms, survival analysis showed that pooled and luminal tumors with high levels of GJA1 mRNA were associated with a better prognostic (hazard ratio < 1), although results were not always statistically significant ( Figure 7 and Figure A7 a,b).…”

“…For instance, a recent study demonstrated that over-expressing Cx43 in two different HER2-positive breast cancer cell lines lead to a diverging ability to proliferate, migrate, form mammospheres and form tumors in mice. Tumorigenic characteristics of the cancer cells were enhanced when functional gap junction channels could not be formed upon Cx43 over-expression, but were reduced when membrane gap junctions plaques allowed cells to communicate [ 34 ]. These aspects of Cx43 biology might explain its different roles according to subtypes but also possibly within subtypes and should therefore be addressed.…”

Connexin 43 Loss Triggers Cell Cycle Entry and Invasion in Non-Neoplastic Breast Epithelium: A Role for Noncanonical Wnt Signaling

“…In the human breast, Cx43 is expressed in luminal epithelial and myoepithelial compartments, while the expression of Cx26 is restricted to the luminal epithelium [7,8]. Altered expression, localization, and function of Cxs have been reported in human breast cancer tissues and in cell lines [9,10,11,12,13,14,15,16] and have been associated with developmental defects in mouse models [17,18,19], suggesting that Cxs have developmental and tumor suppressive roles. Indeed, Cx43 is proposed as an independent prognostic factor in light of its positive correlation with improved disease outcome in breast cancer patients [20,21].…”

Spatial Arrangements of Connexin43 in Cancer Related Cells and Re-Arrangements under Treatment Conditions: Investigations on the Nano-Scale by Super-Resolution Localization Light Microscopy

“…During the process of gap junction reorganization the amount of Cx43 protein not organized in gap junctions is increased [26]. The described dynamic dysregulation of Cx43 is under control of HER2 receptors (also called ErbB receptors), the typical cell proliferation modulators in breast cancer [27]. By the use of advanced co-culture experiments in networks of two-dimensional silicon based microfluidics, it can be demonstrated that tumor organization, gap junction establishment, and intercellular compound transfer are anisotropic and non-random and reflect tumor progression signal spreading along spatial routes decorated with Cx43 containing structures like hemi-channels, gap junctions, connexons and tunneling nanotubes [28].…”