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Background  Understanding the cause of therapeutic resistance and identifying new biomarkers in breast cancer to predict therapeutic responses will help optimise patient care. Calcium (Ca 2+ )-signalling is important in a variety of processes associated with tumour progression, including breast cancer cell migration and proliferation. Ca 2+ -signalling is also linked to the acquisition of multidrug resistance. This study aimed to assess the expression level of proteins involved in Ca 2+ -signalling in an in vitro model of trastuzumab-resistance and to assess the ability of identified targets to reverse resistance and/or act as potential biomarkers for prognosis or therapy outcome.    Methods  Expression levels of a panel of Ca 2+ -pumps, channels and channel regulators were assessed using RT-qPCR in resistant and sensitive age-matched SKBR3 breast cancer cells, established through continuous culture in the absence or presence of trastuzumab. The role of Ca v 3.2 in the acquisition of trastuzumab-resistance was assessed through pharmacological inhibition and induced overexpression. Levels of Ca v 3.2 were assessed in a panel of non-malignant and malignant breast cell lines using RT-qPCR and in patient samples representing different molecular subtypes (PAM50 cohort). Patient survival was also assessed in samples stratified by Ca v 3.2 expression (METABRIC and KM-Plotter cohort).    Results  Increased mRNA of Ca v 3.2 was a feature of both acquired and intrinsic trastuzumab-resistant SKBR3 cells. However, pharmacological inhibition of Ca v 3.2 did not restore trastuzumab-sensitivity nor did Ca v 3.2 overexpression induce the expression of markers associated with resistance, suggesting that Ca v 3.2 is not a driver of trastuzumab-resistance. Ca v 3.2 levels were significantly higher in luminal A, luminal B and HER2-enriched subtypes compared to the basal subtype. High levels of Ca v 3.2 were associated with poor outcome in patients with oestrogen receptor positive (ER+) breast cancers, whereas Ca v 3.2 levels were correlated positively with patient survival after chemotherapy in patients with HER2-positive breast cancers.    Conclusion  Our study identified elevated levels of Ca v 3.2 in trastuzumab-resistant SKBR3 cell lines. Although not a regulator of trastuzumab-resistance in HER2-positive breast cancer cells, Ca v 3.2 may be a potential differential biomarker for survival and treatment response in specific breast cancer subtypes. These studies add to the complex and diverse role of Ca 2+ -signalling in breast cancer progression and treatment.    Electronic supplementary material  The online version of this article (doi:10.1186/s12935-016-0299-0) contains supplementary material, which is available to authorized users.

The voltage gated Ca2+-channel Cav3.2 and therapeutic responses in breast cancer