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Alterations in tropomyosin isoform expression in human transitional cell carcinoma of the urinary bladder
Geraldine Pawlak1, Terence W McGarvey, Trang B Nguyen
1Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
Abstract:
Previous studies of transformed rodent fibroblasts have suggested that specific isoforms of the actin-binding protein tropomyosin (TM) could function as suppressors of transformation, but an analysis of TM expression in patient tumor tissue is limited. The purpose of our study was to characterize expression of the different TM isoforms in human transitional cell carcinoma of the urinary bladder by immunohistochemistry and Western blot analysis. We found that TM1 and TM2 protein levels were markedly reduced and showed >60% reduction in 61% and 55% of tumor samples, respectively. TM5, which was expressed at very low levels in normal bladder mucosa, exhibited aberrant expression in 91% of tumor specimens. The Western blot findings were confirmed by immunohistochemical analysis in a number of tumors. We then investigated the mechanism underlying TM expression deregulation, in the T24 human bladder cancer cell line. We showed that levels of TM1, TM2 and TM3 are reduced in T24 cells, but significantly upregulated by inhibition of the mitogen-activated protein kinase-signaling pathway. In addition, inhibition of this pathway was accompanied by restoration of stress fibers. Overall, changes in TM expression levels seem to be an early event during bladder carcinogenesis. We conclude that alterations in TM isoform expression may provide further insight into malignant transformation in transitional cell carcinomas of the bladder and may be a useful target for early detection strategies.
Insights
Tropomyosin (TM) isoform alterations are early events in bladder cancer. Reduced TM1/TM2 and aberrant TM5 expression in tumors suggest TM changes are key to malignant transformation and potential early detection targets.
Area of Science:
- Cell Biology
- Cancer Research
- Biochemistry
Background:
- Actin-binding proteins like tropomyosin (TM) are implicated in cell transformation.
- Previous studies in rodent models suggest TM isoforms act as tumor suppressors.
- Limited data exists on TM isoform expression in human bladder cancer tissue.
Purpose of the Study:
- To investigate the expression patterns of different tropomyosin (TM) isoforms in human transitional cell carcinoma (TCC) of the urinary bladder.
- To analyze the underlying mechanisms of TM expression deregulation in bladder cancer cells.
- To assess the potential of TM isoforms as biomarkers for early bladder cancer detection.
Main Methods:
- Immunohistochemistry and Western blot analysis were used to examine TM isoform expression in patient tumor samples and a human bladder cancer cell line (T24).
- The study analyzed TM1, TM2, TM3, and TM5 isoforms.
- The mitogen-activated protein kinase (MAPK) signaling pathway was inhibited to study its effect on TM expression and cellular morphology.
Main Results:
- TM1 and TM2 protein levels were significantly reduced in a majority of bladder tumors (>60% reduction in 61% and 55% of samples, respectively).
- TM5 showed aberrant expression in 91% of tumor specimens, contrasting with low levels in normal bladder tissue.
- In the T24 cell line, TM1, TM2, and TM3 levels were reduced but upregulated upon MAPK pathway inhibition, which also restored stress fibers.
Conclusions:
- Alterations in tropomyosin (TM) isoform expression, including reduced TM1/TM2 and aberrant TM5, are observed early in bladder carcinogenesis.
- Deregulation of TM expression in transitional cell carcinoma (TCC) is linked to the MAPK signaling pathway.
- Changes in TM isoform expression may offer insights into malignant transformation and serve as potential targets for early bladder cancer detection strategies.
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