High cell density induces expression from the carbonic anhydrase 9 promoter

Coordinated Regulation of Metabolic Transporters and Migration/Invasion by Carbonic Anhydrase IX

Hypoxia is a prominent feature of the tumor microenvironment (TME) and cancer cells must dynamically adapt their metabolism to survive in these conditions. A major consequence of metabolic rewiring by cancer cells in hypoxia is the accumulation of acidic metabolites, leading to the perturbation of intracellular pH (pHi) homeostasis and increased acidosis in the TME. To mitigate the potentially detrimental consequences of an increasingly hypoxic and acidic TME, cancer cells employ a network of enzymes and transporters to regulate pH, particularly the extracellular facing carbonic anhydrase IX (CAIX) and CAXII. In addition to the role that these CAs play in the regulation of pH, recent proteome-wide analyses have revealed the presence of a complex CAIX interactome in cancer cells with roles in metabolite transport, tumor cell migration and invasion. Here, we explore the potential contributions of these interactions to the metabolic landscape of tumor cells in hypoxia and discuss the role of CAIX as a hub for the coordinated regulation of metabolic, migratory and invasive processes by cancer cells. We also discuss recent work targeting CAIX activity using highly selective small molecule inhibitors and briefly discuss ongoing clinical trials involving SLC-0111, a lead candidate small molecule inhibitor of CAIX/CAXII.

PI3K/Akt activity has variable cell-specific effects on expression of HIF target genes, CA9 and VEGF, in human cancer cell lines

The phosphatidylinositol 3-kinase/Akt (PI3K) pathway regulates hypoxia-inducible factor (HIF) activity. Higher expression of HIF-1alpha and carbonic anhydrase IX (CAIX), a hypoxia-inducible gene, in HT10806TG fibrosarcoma cells (mutant N-ras allele), compared to derivative MCH603 cells (deleted mutant N-ras allele), correlated with increased PI3K activity. Constitutive activation of the PI3K pathway in MCH603/PI3K(act) cells increased HIF-1alpha but, surprisingly, decreased CAIX levels. The cell-type specific inhibitory effect on CAIX was confirmed at the transcriptional level whereas epigenetic modifications of CA9 were ruled out. In summary, our data do not substantiate the generalization that PI3K upregulation leads to increased HIF activity.

Steroid 5α-Reductase Isozymes I and II in Recurrent Prostate Cancer

PURPOSE

Prostate cancer recurs during androgen deprivation therapy despite reduced circulating androgens. We showed that recurrent prostate cancer tissue has testosterone levels similar to androgen-stimulated benign prostate, whereas dihydrotestosterone levels were reduced 82% to 1.45 nmol/L, sufficient for androgen receptor activation. The altered testosterone/dihydrotestosterone ratio in recurrent prostate cancer suggests loss of 5alpha-reducing capability. The aim of this study was to characterize steroid 5alpha-reductase isozymes I (S5alphaRI) and II (S5alphaRII) in prostate tissues.

EXPERIMENTAL DESIGN

A tissue microarray was constructed from 22 recurrent prostate cancer specimens and matched pairs of androgen-stimulated benign prostate and androgen-stimulated prostate cancer from 23 radical prostatectomy specimens. Immunoblots were constructed from eight recurrent prostate cancers, eight androgen-stimulated benign prostate, and eight androgen-stimulated prostate cancer specimens. Isozyme expression was examined in microarray sections and immunoblots using S5alphaRI and S5alphaRII polyclonal antibodies. Isozyme activities were measured in 12 recurrent prostate cancer, 12 androgen-stimulated benign prostate, and 12 androgen-stimulated prostate cancer specimens.

RESULTS

Nuclear immunostaining exhibited higher S5alphaRI expression than S5alphaRII in recurrent prostate cancer, androgen-stimulated benign prostate, and androgen-stimulated prostate cancers (P < 0.0001); mean expression was 125, 150, and 115 for S5alphaRI versus 10, 29, and 37 for S5alphaRII, respectively. Cytoplasmic immunostaining was moderate and similar for both isozymes in the three tissue types (P > 0.05). Immunoblots confirmed immunohistochemistry; S5alphaRI was expressed in recurrent prostate cancer specimens and S5alphaRII was not detected. The activity of S5alphaRI (114.4 pmol/mg epithelial protein/minute) was 3.7-fold higher than S5alphaRII (30.7 pmol/mg epithelial protein/minute) in recurrent prostate cancer specimens.

CONCLUSIONS

Expression levels and isozyme activity shifts from S5alphaRII toward S5alphaRI in recurrent prostate cancer. Dual inhibition of S5alphaRI and S5alphaRII should reduce dihydrotestosterone biosynthesis and may prevent or delay growth of recurrent prostate cancer.

Characterization of carbonic anhydrase IX (CA IX) as an endogenous marker of chronic hypoxia in live human tumor cells

PURPOSE

Published clinical studies provide conflicting data regarding the prognostic significance of carbonic anhydrase IX (CA IX) overexpression as an endogenous marker of tumor hypoxia and its comparability with other methods of hypoxia detection. We performed a systematic analysis of CA IX protein levels under various in vitro conditions of tumor hypoxia in HT 1080 human fibrosarcoma and FaDu human pharyngeal carcinoma cells. Because sorting of live CA IX positive cells from tumors provides a tool to study the radiosensitivity of chronically hypoxic cells, we modified and tested a CA IX flow cytometry protocol on mixed hypoxic/aerobic suspensions of HT 1080 and FaDu cells.

METHODS AND MATERIALS

HT 1080 and FaDu cells were treated with up to 24 h of in vitro hypoxia and up to 96 h of reoxygenation. To test the effect of nonhypoxic stimuli, glucose and serum availability, pH and cell density were modified. CA IX protein was quantified in Western blots of whole-cell lysates. Mixed suspensions with known percentages of hypoxic cells were prepared for CA IX flow cytometry. The same mixtures were assayed for clonogenic survival after 10 Gy.

RESULTS

Hypoxia-induced CA IX protein expression was seen after >6 h at < or =5% O(2), and protein was stable over 96 h of reoxygenation in both cell lines. Glucose deprivation abolished the hypoxic CA IX response, and high cell density caused CA IX induction under aerobic conditions. Measured percentages of CA IX-positive cells in mixtures closely reflected known percentages of hypoxic cells in HT 1080 and were associated with radioresistance of mixtures after 10 Gy.

CONCLUSION

CA IX is a stable marker of current or previous chronic hypoxia but influenced by nonhypoxic stimuli. Except the time course of accumulation, all properties of this marker resembled our previous findings for hypoxia-inducible factor-1alpha. A modified flow cytometry protocol provided good separability of CA IX-negative and -positive cells in vitro and can be applied to sort chronically hypoxic cells from tumors.