Disrupting Hypoxia-Induced Bicarbonate Transport Acidifies Tumor Cells and Suppresses Tumor Growth

Intervertebral disc degeneration is a ubiquitous condition closely linked to chronic low-back pain. The health of the avascular nucleus pulposus (NP) plays a crucial role in the development of this pathology. We tested the hypothesis that a network comprising HIF-1α, carbonic anhydrase (CA) 9 and 12 isoforms, and sodium-coupled bicarbonate cotransporters (NBCs) buffer intracellular pH through coordinated bicarbonate recycling. Contrary to the current understanding of NP cell metabolism, analysis of metabolic-flux data from Seahorse XF analyzer showed that CO hydration contributes a significant source of extracellular proton production in NP cells, with a smaller input from glycolysis. Because enzymatic hydration of CO is catalyzed by plasma membrane-associated CAs we measured their expression and function in NP tissue. NP cells robustly expressed isoforms CA9/12, which were hypoxia-inducible. In addition to increased mRNA stability under hypoxia, we observed binding of HIF-1α to select hypoxia-responsive elements on CA9/12 promoters using genomic chromatin immunoprecipitation. Importantly, in vitro loss of function studies and analysis of discs from NP-specific HIF-1α null mice confirmed the dependency of CA9/12 expression on HIF-1α. As expected, inhibition of CA activity decreased extracellular acidification rate independent of changes in HIF activity or lactate/H efflux. Surprisingly, CA inhibition resulted in a concomitant decrease in intracellular pH that was mirrored by inhibition of sodium-bicarbonate importers. These results suggested that extracellular bicarbonate generated by CA9/12 is recycled to buffer cytosolic pH fluctuations. Importantly, long-term intracellular acidification from CA inhibition lead to compromised cell viability, suggesting that plasma-membrane proton extrusion pathways alone are not sufficient to maintain homeostatic pH in NP cells. Taken together, our studies show for the first time that bicarbonate buffering through the HIF-1α-CA axis is critical for NP cell survival in the hypoxic niche of the intervertebral disc. © 2017 American Society for Bone and Mineral Research.

show abstract

“…In some hypoxic cancer cells CA9/12 produced extracellular HCO 3 − is retrieved to buffer cytosolic pH (19, 55) (Fig. 9A).…”

Section: Resultsmentioning

confidence: 99%

Bicarbonate Recycling by HIF-1–Dependent Carbonic Anhydrase Isoforms 9 and 12 Is Critical in Maintaining Intracellular pH and Viability of Nucleus Pulposus Cells

Silagi

Schoepflin

Seifert

et al. 2017

Journal of Bone and Mineral Research

View full text Add to dashboard Cite

show abstract

“…A recent report demonstrated that genetic targeting of sodium bicarbonate transporters with siRNA could decrease the growth of U87 GBM cells in vitro and in vivo (51). These data suggest that it will be important to consider the entire carbonic anhydrase-bicarbonate transporter system and its effects on TMZ treatment in the future.…”

Section: Discussionmentioning

confidence: 99%

Addition of carbonic anhydrase 9 inhibitor SLC-0111 to temozolomide treatment delays glioblastoma growth in vivo

Boyd¹,

Walker²,

Fried³

et al. 2017

JCI Insight

103

View full text Add to dashboard Cite

“…It is generally reported that HIF-1α is constitutively expressed in many solid tumors2526. HIF-1 regulate hundreds of downstream genes, most of which are closely related to tumor growth, metastasis, and invasion27, as well as chemoresistance and radioresistance28.…”

Section: Discussionmentioning

confidence: 99%

Brusatol inhibits HIF-1 signaling pathway and suppresses glucose uptake under hypoxic conditions in HCT116 cells

Shi

et al. 2016

Sci Rep

View full text Add to dashboard Cite

Hypoxia-inducible factor-1 (HIF-1) is an important transcription factor that induces adaptive responses upon low oxygen conditions in human cancers and triggers off a poor prognostic outcome of conventional treatments. In this study, we discovered for the first time that brusatol (BRU), a quassinoid extracted from Brucea Esters, has the capability to inhibit HIF-1 signaling pathway. We found that BRU concentration-dependently down-regulated HIF-1α protein levels under hypoxia or CoCl2-induced mimic hypoxia in HCT116 cells without causing significant cytotoxicity. Besides, the transactivation activity of HIF-1 was suppressed by BRU under hypoxic conditions, as well as the expression of HIF-1 target genes, including VEGF, GLUT1, HK2 and LDHA. In addition, BRU can also decrease glucose consumption under hypoxia through inhibition of HIF-1 signaling pathway. Further studies revealed that the inhibitory effect of BRU on HIF-1 signaling pathway might be attributed to promoting degradation of HIF-1α. Interestingly, intracellular reactive oxygen species (ROS) levels and mitochondrial ROS level were both decreased by BRU treatment, indicating the involvment of mitochondrial ROS regulation in the action of BRU. Taken together, these results provided clear evidence for BRU-mediated HIF-1α regulation and suggested its therapeutic potential in colon tumors.

show abstract

Disrupting Hypoxia-Induced Bicarbonate Transport Acidifies Tumor Cells and Suppresses Tumor Growth

Cited by 89 publications

References 46 publications

Bicarbonate Recycling by HIF-1–Dependent Carbonic Anhydrase Isoforms 9 and 12 Is Critical in Maintaining Intracellular pH and Viability of Nucleus Pulposus Cells

Bicarbonate Recycling by HIF-1–Dependent Carbonic Anhydrase Isoforms 9 and 12 Is Critical in Maintaining Intracellular pH and Viability of Nucleus Pulposus Cells

Addition of carbonic anhydrase 9 inhibitor SLC-0111 to temozolomide treatment delays glioblastoma growth in vivo

Brusatol inhibits HIF-1 signaling pathway and suppresses glucose uptake under hypoxic conditions in HCT116 cells

Contact Info

Product

Resources

About