Contribution of Na+,HCO3(-)-cotransport to cellular pH control in human breast cancer: a role for the breast cancer susceptibility locus NBCn1 (SLC4A7).
Genome-wide association studies recently linked the locus for Na(+),HCO(3)(-)-cotransporter NBCn1 (SLC4A7) to breast cancer susceptibility, yet functional insights have been lacking. To determine whether NBCn1, by transporting HCO(3)(-) into cells, may dispose of acid produced during high metabolic activity, we studied the expression of NBCn1 and the functional impact of Na(+),HCO(3)(-)-cotransport in human breast cancer. We found that the plasmalemmal density of NBCn1 was 20-30% higher in primary breast carcinomas and metastases compared to matched normal breast tissue. The increase in NBCn1 density was similar in magnitude to that observed for Na(+)/H(+)-exchanger NHE1 (SLC9A1), a transporter previously implicated in cell migration, proliferation and malignancy. In primary breast carcinomas, the apparent molecular weight for NBCn1 was increased compared to normal tissue. Using pH-sensitive fluorophores, we showed that Na(+),HCO(3)(-)-cotransport is the predominant mechanism of acid extrusion and is inhibited 34 ± 9% by 200 μM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid in human primary breast carcinomas. At intracellular pH (pH(i) ) levels >6.6, CO(2)/HCO(3)(-)-dependent mechanisms accounted for >90% of total net acid extrusion. Na(+)/H(+)-exchange activity was prominent only at lower pH(i) -values. Furthermore, steady-state pH(i) was 0.35 ± 0.06 units lower in the absence than in the presence of CO(2)/HCO(3)(-). In conclusion, expression of NBCn1 is upregulated in human primary breast carcinomas and metastases compared to normal breast tissue. Na(+),HCO(3)(-)-cotransport is a major determinant of pH(i) in breast cancer and the modest DIDS-sensitivity is consistent with NBCn1 being predominantly responsible. Hence, our results suggest a major pathophysiological role for NBCn1 that may be clinically relevant.
Department of Biomedicine, Aarhus University, Denmark. eb@fi.au.dk.
Ebbe
E
Boedtkjer
José M A
JM
Moreira
Marco
M
Mele
Pernille
P
Vahl
Vera T
VT
Wielenga
Peer M
PM
Christiansen
Vibeke E D
VE
Jensen
Stine F
SF
Pedersen
Christian
C
Aalkjaer
D001943:Breast Neoplasms / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D012333:RNA, Messenger / Q000032:analysis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000502:physiology; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000502:physiology*; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics
D027682:Cation Transport Proteins; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D027982:Sodium-Bicarbonate Symporters; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; C422022:SLC4A7 protein, human; C490998:SLC9A1 protein, human; C508053:ERBB2 protein, human