The goals of this study were to determine the expression of
metallothionein isoform 1 and 2
proteins (MT-1 and MT-2) in
bladder cancer and then to determine which MT
isoform-specific genes promoted the expression of these
proteins. Immunohistochemical analysis disclosed no immunoreactivity for MT-1 and MT-2 (designated as MT-1/2 to reflect the nonspecificity of the antibody for the two
isoforms) in cells comprising the normal bladder or in nonmalignant bladder disorders, such as
cystitis and
interstitial cystitis. Immunohistochemical analysis demonstrated that MT-1/2 was overexpressed in all samples of
carcinoma in situ and in high-grade
bladder cancer, with variable overexpression in low-grade
bladder cancer and dysplastic lesions. The intensity and frequency of MT-1/2 staining correlated with the grade of the
tumor. The MT-1 and MT-2
proteins are encoded by a family of eight genes (MT-1A, MT-1B, MT-1E, MT-1F, MT-1G, MT-IH, MT-1X, and MT-2A), and
reverse transcriptase-polymerase chain reaction was used to determine which genes were expressed in the normal bladder and in
bladder cancer. This analysis demonstrated that both normal and cancerous bladder tissue expressed
mRNA for the MT-2A and
MT-1X genes. The expression of MT-1E
mRNA was variable in both normal bladder and
bladder cancer specimens. Comparison of expression relative to that of
beta-actin demonstrated that the level of
MT-1X mRNA was overexpressed greatly in
bladder cancer as compared to the level in normal bladder tissue. In contrast, the level of MT-2A
mRNA was similar in both the normal and the
bladder cancer specimens. The level of
MT-1X expression did not vary with
tumor grade. These studies suggest that the overexpression of MT-1/2
protein in
bladder cancer is a result of the overexpression of the
MT-1X gene.