ErbB2 upregulates the Na⁺,HCO₃^‐‐cotransporter NBCn1/SLC4A7in human breast cancer cellsviaAkt, ERK, Src, and Krüppel‐like factor 4

Abstract

Misregulation of acid-base transport plays central roles in cancer development. We previously demonstrated the strong up-regulation of the Na(+),HCO3(-) cotransporter NBCn1 (SLC4A7) in MCF-7 breast cancer cells by a truncated, constitutively active ErbB2 (HER2) receptor, ΔNErbB2, and showed that NBCn1 expression and activity are increased in breast cancer tissue from patients. Here, we present the first in-depth characterization of an SLC4A7 promoter and identify its minimal ΔNErbB2-sensitive region. Inhibition or siRNA-mediated knockdown of PI3K, Akt1, ERK1/2, or Src decreased the NBCn1 protein level in ΔNErbB2-expressing MCF-7 cells by ~50, 60, 30 and 35%, respectively. Further, knockdown of the transcription factor Krüppel-like factor 4 (KLF4) reduced NBCn1 protein expression by ~40%, and KLF4 overexpression increased NBCn1 expression by 50-80%. In contrast, knockdown of the closely related transcription factor specificity protein 1 (Sp1) or transfection with dominant-negative Sp1 increased NBCn1 expression by ~35 and ~50%, respectively. NBCn1 expression was also increased by stimulation of full-length ErbB1, -2, and -3 receptors in SKBr3 cells (1.5- and 2-fold by NRG1 or EGF, respectively) or after their exogenous expression in MCF-7 cells. Finally, stimulation with NRG1 or EGF more than doubled acid extrusion capacity in SKBr3 cells. In conclusion, NBCn1 is strongly upregulated by ErbB receptor signaling in a manner involving opposite effects of KLF4 and Sp1, transcription factors with central roles in cancer development. ErbB-induced up-regulation of NBCn1-mediated acid extrusion may play important physiological and pathophysiological roles in the breast epithelium and other tissues with high ErbB receptor levels.

Constitutively Active ErbB2 Regulates Cisplatin-Induced Cell Death in Breast Cancer Cells via Pro- and Antiapoptotic Mechanisms

“…Both STAT3 and KLF4 have been assigned roles in activation of CDKN1A (the gene coding for p21) promoter (13), and we have previously shown both to be activated by DNErbB2 expression (32). That cisplatin treatment strongly attenuated STAT3 phosphorylation in DNErbB2-expressing cells while having no effect on p21 argues against a role for STAT3 in this context, leaving KLF4 as a hypothetical candidate, to be tested in future studies.…”

Disrupting Na+,HCO3–-cotransporter NBCn1 (Slc4a7) delays murine breast cancer development

“…25,27 This mechanism may also contribute to NBCn1 upregulation in the current model of breast carcinogenesis because ErbB2 phosphorylation was increased in breast cancer compared with normal breast tissue. In congruence, levels of ErbB2 phosphorylation and NBCn1 expression were both independent of tumor volume.…”

“…However, the difference in glycolytic activity between breast cancer from WT and NBCn1 KO mice is at least partly explained by differences in tumor size: the [lactate]/[glucose]-ratio increases as a function of breast tumor size(Figure 5c, right panel) consistent with higher flow of glucose to lactate in larger compared with smaller breast tumors 24. We observed no differences in [pyruvate] or [glycerol] between breast tumors and matched normal breast tissue or between tissue from NBCn1 KO and WT mice(Figures 5d and e).Cell signaling is modified by breast carcinogenesis and NBCn1 KO ErbB2 signaling upregulates NBCn1 expression in cultured MCF-7 breast cancer cells [25][26][27]. Consistent with the increased NBCn1 expression levels in tumors, we found higher levels of phosphorylated ErbB2 in breast cancer compared with matched normal breast tissue(Figure 6a, left panel).…”

When Good Turns Bad: Regulation of Invasion and Metastasis by ErbB2 Receptor Tyrosine Kinase

“…Simplified presentation of invasion and migration inducing molecular mechanisms and signaling pathways, mainly based on studies done with ErbB2 and p95 ErbB2 expressing MCF7 and MCF10A cells [21,48,52,53,82,83,89,90,97,98,99,100,101,102,103,104,105,106]. …”

“…The basal levels of MMP-1 and MMP-9 are increased in various breast cancer cells, including MCF7, in response to heregulin-β1 via activation of MAPK/ERK pathway [127] and overexpression of Ets1 in ErbB2 expressing breast cancer cells increases the expression of MMP-1 [128]. One potentially important p95 ErbB2 upregulated protein in MCF7 cells is the Na(+),HCO(3)(-)-cotransporter NBCn1/SLC4A7 that is involved in the acid extrusion and acidification of the extracellular space [104,105]. Moreover, overespression of p95 ErbB2 activates the Na + /H + exchanger NHE1 resulting in its localization to invadopodies contributing to the acidification of the extracellular space [54].…”