Expression and functional influence of cellular retinoic acid-binding protein II in renal cell carcinoma.
BACKGROUND
Retinoic acid (RA) and its derivates possess antiproliferative and tumor-suppressive abilities and are successfully used in the treatment of various malignancies. However, in metastatic renal cell carcinoma (RCC), its application did not meet first expectations. As the exact mechanisms of RA action and especially the role of the cellular retinoic acid-binding proteins (CRABP) still remain unclear, we studied the expression of CRABP-II and its potential influence on RA response in RCC.


METHODS
We used the real-time RT-PCR methodology to investigate CRABP-II expression in 12 RCC samples and corresponding normal kidney tissue. Moreover, CRABP-II was cloned and overexpressed in CAKI-2 RCC cells. CRABP-II (un)transfected CAKI-2 cells were stimulated with all-trans RA (ATRA) and 9-cis RA, and their antiproliferative effects were evaluated using 3H-thymidine-proliferation assays.


RESULTS
Using RPS9 and RPLP0 to normalize its expression, the median tumor/kidney ratio for CRABP-II expression was 0.16 and 0.12, respectively. Using proliferation assays, CRABP-II overexpressing CAKI-2 cells did not exhibit a significant change in RA sensitivity, but appeared to be less sensitive toward RA-stimulation compared to CAKI-2 cells expressing naturally low levels of CRABP-II (maximum difference, 59% at 3 microM ATRA).


CONCLUSIONS
We were able to demonstrate a downregulation of CRABP-II expression in primary RCC tumor samples compared to the corresponding normal kidney tissue. However, CRABP-II overexpression in CAKI-2 RCC cells did not significantly influence RA associated antiproliferative actions. Further experiments are necessary to define the exact role of CRABP-II and its downregulation in RCC including its influence and dependence on other molecules involved in RA signalling and metabolism.
Goelden
Ulrike
U
Department of Cell Biology and Immunology, German Research Centre for Biotechnology, Braunschweig, Germany.
Pfoertner
Susanne
S
Hansen
Wiebke
W
Toepfer
Tanja
T
von Knobloch
Rolf
R
Hofmann
Rainer
R
Buer
Jan
J
Schrader
Andres Jan
AJ
D000368:Aged; D002292:Carcinoma, Renal Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D005819:Genetic Markers; D006801:Humans; D066298:In Vitro Techniques; D007680:Kidney Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics*; D018168:Receptors, Retinoic Acid / Q000096:biosynthesis / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D005819:Genetic Markers; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; C082928:retinoic acid binding protein II, cellular