Clinical Significance of Tumor Suppressor PTEN in Colorectal Carcinoma

Background: It has been demonstrated that the deletion, mutation, hypermethylation and subcellular location of the tumor suppressor phosphatase and tensin homologue (PTEN) are closely correlated with carcinogenesis, progression and prognosis of malignancy. Both mutation and the microsatellite instability of the PTEN gene influence regulation of the PI3K/Akt signaling pathway. This study investigated whether loss of nuclear PTEN is correlated with chemosensitivity, clinicopathological parameters and survival.

Methods: Intracellular levels of PTEN of multiple cell lines of colorectal carcinoma (CRC) were evaluated by Western blotting and immunocytochemistry. The chemosensitivity of cell lines with various expression levels of PTEN was evaluated using 5-flurouracil (5-FU), oxaliplatin and irinotecan (CPT), and clinical significance was evaluated by immunohistochemical analysis of 133 CRC specimens.

Results: Colon cancer cell lines HT-29, LoVo and SW480 differed in expression of PTEN, with high, moderate and low levels, respectively. HT-29 and LoVo PTEN expression was suppressed by a low concentration of 5-FU and oxaliplatin; however, SW480 was insensitive to these chemotherapeutic agents. Nuclear PTEN was overexpressed in most (>80%) normal colon mucosa samples, but the incidence significantly decreased (89.2% → 53.4%) in the CRC group. PTEN in the nucleus was negatively correlated with tumor size and vascular invasion in CRC, and CRC patients with negative PTEN expression in the nucleus exhibited poor survival.

Conclusion: Cell lines with a high expression of PTEN are sensitive to chemotherapy with 5-FU and oxaliplatin. Nuclear PTEN expression gradually decreases after malignant transformation, and loss of PTEN expression in the nucleus is associated with tumor progression and poor clinical outcome in CRC.