DIFFERENTIAL GENE EXPRESSION IN PROSTATE CANCER Identification of genes expressed in prostate cancer, androgen- dependent and androgen-independent LNCaP cell lines, and characterization of TMPRSS2 expression

Prostate cancer is the most common solid tumor among men in Western industrialized countries. A major problem in prostate cancer treatment is the development of androgen-independence, as androgen-deprivation therapy is the basic therapy for the disease. Molecular mechanisms behind prostate cancer and androgen-independent growth development are poorly known. In this study, subtractive hybridization was used for the generation of a cDNA library specific for prostate cancer. Analysis of the cDNA library revealed over-expression of several ribosomal proteins namely L4, L5, L7a, L23a, L30, L37, S14 and S18, in prostate cancer cell lines. Overexpression of L7a and L37 was also confirmed in prostate cancer tissue samples. Further, cDNA array was used in order to examine differentially expressed genes in androgendependent and androgen-independent prostate cancer cell line LNCaP. Monoamine oxidase A, an Expressed Sequence Tag (EST) similar to rat P044, and EST AA412049 were highly overexpressed in androgen-dependent LNCaP cells. Tissue-type plasminogen activator, interferoninducible protein p78 (MxB), an EST similar to galectin-1, follistatin, fatty acid-binding protein 5, EST AA609749, annexin I, the interferon-inducible gene 1-8U and phospholipase D1 were highly over-expressed in androgen-independent LNCaP cells. The EST similar to rat P044, the EST similar to galectin-1, follistatin, annexin I and the interferon-inducible gene 1-8U were also expressed in benign prostatic hyperplasia tissue. The Y-linked ribosomal protein S4, Mat-8, and EST AA307912 were highly expressed in benign prostatic hyperplasia tissue. In situ hybridization of mouse embryos and adult mouse tissues revealed the expression of TMPRSS2 in the epithelium throughout the gastrointestinal, urogenital and respiratory tracts during development. In human multiple tissue RNA dot blot, the highest level of expression was detected in prostate, and lower levels in colon, stomach and salivary gland. TMPRSS2 transcript levels were significantly higher in prostate cancer tissue between benign and malignant epithelium of prostate cancer patients with untreated disease. Similarly, in poorly differentiated adenocarcinomas, expression in malignant tissue was significantly higher. Enzymatic mutation detection and direct sequencing of TMPRSS2 coding region revealed only one deletion in aggressive disease among 9 non-aggressive and 9 aggressive prostate cancer samples. No other mutations were found. Detected 7-base pair deletion leads to premature stop codon and disruption of serine protease substrate binding and catalytic active site. We cloned several potential genes whose expression is changed during prostate cancer initiation or progression. These genes may serve as prostate cancer markers, and further studies are needed to clarify the expression of these proteins during the disease.