12-17-2013, 10:03 PM
On this forum, we have previously reported on the potential of the zebrafish as a model organism for drug discovery, following the entry into Phase II trials of ProHema, the first drug to be developed using zebrafish (http://www.biotechnologyforums.com/thread-2562.html). This potential apparently extends to zebrafish embryos, following the publication last week of a paper from the laboratory of Dr. C. Duan of the University of Michigan in the journal Cell Death and Differentiation. The study used zebrafish embryos to examine the role of calcium deficiency in epithelial cell proliferation and colon cancer risk. It uncovered a novel interaction between low calcium availability, the calcium transport channels TRPV5/6 and activation of the growth factor pathway insulin growth factor 1 receptor (IGF1R)-PI3K-Akt.
TRPV5 and 6 are members of the superfamily of transient receptor potential (TRP) channels, subfamily vanilloid. They are mainly expressed in epithelia of organs including digestive tract, kidney, testis, ovaries and skin. Up-regulation of TRPV5/6 expression has been correlated to progression of a number of different cancers including prostate, colon, breast, thyroid, and ovarian. Chemical inhibitors of TRPV6 have been proposed as potential drug candidates in cancers of epithelial origin while TRPV6 silencing has been shown to reduce basal calcium influx and cell proliferation in breast cancer cell lines. Microarray analysis indicated that TRPV6 is up-regulated in estrogen receptor (ER)-negative breast tumours and in HER2-positive tumours and that high TRPV6 levels was correlated to decreased survival. However, the mechanism of how TRPV5/6 might be involved in, for example, cell proliferation is poorly understood. Calcium deficiency has also been correlated to development of epithelial cancers such as colon and breast cancer, again via poorly understood mechanisms.
Dr Duan’s group exploited the fact that zebrafish embryo skin contains accessible Ca2+-transporting epithelial cells known as ionocytes. This offers an advantage over other models where the calcium-importing epithelial cells lie chiefly in internal organs. The numbers of ionocytes in zebrafish embryos increase significantly when the embyos are placed in a low calcium ion environment. By using BrdU pulse-labelling experiments, the group showed that pre-existing ionocytes re-entered the cell cycle in response to low calcium ion concentration and underwent a strong, sustained activation of the of IGF1R-PI3K-Akt signalling pathway. The ionocytes were shown to express both the IGF binding protein, Igfbp5a and the Ca2+-selective channel Trpv5/6. Knock-down or chemical inhibition experiments showed that inhibition of Igfbp5a, IGF1 receptor, PI3K, and Akt attenuated low calcium induced ionocyte proliferation. Moreover, although inhibition of Trpv5/6 resulted in elevated pAkt levels and increased ionocyte proliferation in the presence of normal calcium levels, when calcium was depleted, TrpV5/6 inhibition induced Akt activation. Having established these results in zebrafish embryos, the group then turned their attention to human colon cancer cells and showed that, just in the zebrafish ionocytes, low calcium induced PI3K-PDK1-Akt signalling in a TRPV6-dependent manner.
The study authors conclude that their results indicate a novel and evolutionarily conserved signalling interaction that sheds light on the abnormal epithelial proliferation associated with Ca2+ deficiency. Understanding this mechanism opens the way for future drug development.
Sources
BOLANZ, K.A., KOVACS, G.G., LANDOWSKI, C.P. and HEDIGER, M.A., 2009. Tamoxifen inhibits TRPV6 activity via estrogen receptor-independent pathways in TRPV6-expressing MCF-7 breast cancer cells. Molecular Cancer Research: MCR, 7(12), pp. 2000-2010.
DAI, W., BAI, Y., HEBDA, L., ZHONG, X., LIU, J., KAO, J. and DUAN, C., 2013. Calcium deficiency-induced and TRP channel-regulated IGF1R-PI3K-Akt signaling regulates abnormal epithelial cell proliferation. Cell death and differentiation, 2013
HU, H., BANDELL, M., GRANDL, J. and PETRUS, M., 2011. High-Throughput Approaches to Studying Mechanisms of TRP Channel Activation. TRP Channels, .
KONDRATSKYI, A., YASSINE, M., KONDRATSKA, K., SKRYMA, R., SLOMIANNY, C. and PREVARSKAYA, N., 2013. Calcium-permeable ion channels in control of autophagy and cancer. Frontiers In Physiology, 4, pp. 272-272.
LANDOWSKI, C.P., BOLANZ, K.A., SUZUKI, Y. and HEDIGER, M.A., 2011. Chemical inhibitors of the calcium entry channel TRPV6. Pharmaceutical Research, 28(2), pp. 322-330.
LEHEN'KYI, V., RAPHAëL, M. and PREVARSKAYA, N., 2012. The role of the TRPV6 channel in cancer. The Journal of Physiology, 590, pp. 1369-1376.
PETERS, A.A., SIMPSON, P.T., BASSETT, J.J., LEE, J.M., DA SILVA, L., REID, L.E., SONG, S., PARAT, M., LAKHANI, S.R., KENNY, P.A., ROBERTS-THOMSON, S. and MONTEITH, G.R., 2012. Calcium channel TRPV6 as a potential therapeutic target in estrogen receptor-negative breast cancer. Molecular Cancer Therapeutics, 11(10), pp. 2158-2168.
ZHENG, Y., ZHOU, H., MODZELEWSKI, J.R.K., KALAK, R., BLAIR, J.M., SEIBEL, M.J. and DUNSTAN, C.R., 2007. Accelerated bone resorption, due to dietary calcium deficiency, promotes breast cancer tumor growth in bone. Cancer research, 67(19), pp. 9542-9548.
TRPV5 and 6 are members of the superfamily of transient receptor potential (TRP) channels, subfamily vanilloid. They are mainly expressed in epithelia of organs including digestive tract, kidney, testis, ovaries and skin. Up-regulation of TRPV5/6 expression has been correlated to progression of a number of different cancers including prostate, colon, breast, thyroid, and ovarian. Chemical inhibitors of TRPV6 have been proposed as potential drug candidates in cancers of epithelial origin while TRPV6 silencing has been shown to reduce basal calcium influx and cell proliferation in breast cancer cell lines. Microarray analysis indicated that TRPV6 is up-regulated in estrogen receptor (ER)-negative breast tumours and in HER2-positive tumours and that high TRPV6 levels was correlated to decreased survival. However, the mechanism of how TRPV5/6 might be involved in, for example, cell proliferation is poorly understood. Calcium deficiency has also been correlated to development of epithelial cancers such as colon and breast cancer, again via poorly understood mechanisms.
Dr Duan’s group exploited the fact that zebrafish embryo skin contains accessible Ca2+-transporting epithelial cells known as ionocytes. This offers an advantage over other models where the calcium-importing epithelial cells lie chiefly in internal organs. The numbers of ionocytes in zebrafish embryos increase significantly when the embyos are placed in a low calcium ion environment. By using BrdU pulse-labelling experiments, the group showed that pre-existing ionocytes re-entered the cell cycle in response to low calcium ion concentration and underwent a strong, sustained activation of the of IGF1R-PI3K-Akt signalling pathway. The ionocytes were shown to express both the IGF binding protein, Igfbp5a and the Ca2+-selective channel Trpv5/6. Knock-down or chemical inhibition experiments showed that inhibition of Igfbp5a, IGF1 receptor, PI3K, and Akt attenuated low calcium induced ionocyte proliferation. Moreover, although inhibition of Trpv5/6 resulted in elevated pAkt levels and increased ionocyte proliferation in the presence of normal calcium levels, when calcium was depleted, TrpV5/6 inhibition induced Akt activation. Having established these results in zebrafish embryos, the group then turned their attention to human colon cancer cells and showed that, just in the zebrafish ionocytes, low calcium induced PI3K-PDK1-Akt signalling in a TRPV6-dependent manner.
The study authors conclude that their results indicate a novel and evolutionarily conserved signalling interaction that sheds light on the abnormal epithelial proliferation associated with Ca2+ deficiency. Understanding this mechanism opens the way for future drug development.
Sources
BOLANZ, K.A., KOVACS, G.G., LANDOWSKI, C.P. and HEDIGER, M.A., 2009. Tamoxifen inhibits TRPV6 activity via estrogen receptor-independent pathways in TRPV6-expressing MCF-7 breast cancer cells. Molecular Cancer Research: MCR, 7(12), pp. 2000-2010.
DAI, W., BAI, Y., HEBDA, L., ZHONG, X., LIU, J., KAO, J. and DUAN, C., 2013. Calcium deficiency-induced and TRP channel-regulated IGF1R-PI3K-Akt signaling regulates abnormal epithelial cell proliferation. Cell death and differentiation, 2013
HU, H., BANDELL, M., GRANDL, J. and PETRUS, M., 2011. High-Throughput Approaches to Studying Mechanisms of TRP Channel Activation. TRP Channels, .
KONDRATSKYI, A., YASSINE, M., KONDRATSKA, K., SKRYMA, R., SLOMIANNY, C. and PREVARSKAYA, N., 2013. Calcium-permeable ion channels in control of autophagy and cancer. Frontiers In Physiology, 4, pp. 272-272.
LANDOWSKI, C.P., BOLANZ, K.A., SUZUKI, Y. and HEDIGER, M.A., 2011. Chemical inhibitors of the calcium entry channel TRPV6. Pharmaceutical Research, 28(2), pp. 322-330.
LEHEN'KYI, V., RAPHAëL, M. and PREVARSKAYA, N., 2012. The role of the TRPV6 channel in cancer. The Journal of Physiology, 590, pp. 1369-1376.
PETERS, A.A., SIMPSON, P.T., BASSETT, J.J., LEE, J.M., DA SILVA, L., REID, L.E., SONG, S., PARAT, M., LAKHANI, S.R., KENNY, P.A., ROBERTS-THOMSON, S. and MONTEITH, G.R., 2012. Calcium channel TRPV6 as a potential therapeutic target in estrogen receptor-negative breast cancer. Molecular Cancer Therapeutics, 11(10), pp. 2158-2168.
ZHENG, Y., ZHOU, H., MODZELEWSKI, J.R.K., KALAK, R., BLAIR, J.M., SEIBEL, M.J. and DUNSTAN, C.R., 2007. Accelerated bone resorption, due to dietary calcium deficiency, promotes breast cancer tumor growth in bone. Cancer research, 67(19), pp. 9542-9548.
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