Objective: To investigate the expression of insulin receptor isoforms (IR, including IR-A and IR-B) in endometrial carcinoma (EC), and explore the role of IR-A in the growth of endometrial carcinoma cells.
Methods: The expression of IR isoforms were detected by reverse transcription (RT)-PCR and real-time PCR in 4 different endometrial cancer cell lines (HEC-1-A, Ishikawa, RL95-2 and KLE), with human breast cancer cell line MCF-7 cells and hepatocellular carcinoma cell line Hep-G2 as positive control and in the endometrial cancer tissue specimens of 42 cases, admitted in Peking University People's Hospital from November 2007 to July 2009, with normal endometrial tissues from 15 cases of ovarian neoplasms at the same period as controls. The relationships among the expression of IR, IR-A isoforms and the clinicopathological parameters of EC tissues were analyzed by Spearman rank correlation analysis. An eukaryotic IR-A expression plasmid was constructed and transfected into RL95-2 cells [RL95-2(IR-A)] for overexpression of IR-A in RL95-2 cells, in which the expression of IR-A originally was low. Non radioactive cell proliferation assay-MTS was used to determine the proliferation curves in the four EC cells listed above and in RL95-2 or RL95-2 (IR-A).
Results: (1) There were two isoforms of IR-A and IR-B co-expressed were detected in EC cells and EC tissues. Among four kinds of EC cell lines, the expression level of IR mRNA in RL95-2 cells was the highest, followed by Ishikawa, KLE and HEC-1-A cells, in which the relative IR mRNA expression levels were (26.54 ± 1.82)×10(-4), (15.44 ± 3.29)×10(-4), (10.14 ± 0.10)×10(-4) and (2.63 ± 0.23)×10(-4), respectively (P < 0.01). The expression level of IR-A mRNA was the highest in Ishikawa cells, followed by KLE, RL95-2 and HEC-1-A cells, with the relative expression levels were (12.07 ± 3.31)×10(-4), (4.68 ± 0.63)×10(-4), (3.03 ± 0.22)×10(-4) and(1.46 ± 0.03)×10(-4), respectively (P < 0.01). The relative expression level of IR and IR-A mRNA were 0.017 ± 0.013 and 0.011 ± 0.010 in the EC tissues, respectively, compared with 0.015 ± 0.014 and 0.010 ± 0.012 in the controls, in which there were no significant differences in the expression level of IR or IR-A mRNA between EC tissues and the control (P = 0.662, P = 0.780). The expression of IR and IR-A in EC tissues had no significant relevance with International Federation of Gynecology and Obstetrics (FIGO) stage, cell differentiation, depth of myometrial invasion, invasion of lymph-vascular space, lymph nodes metastasis, the expression status of estrogen receptor, human progesterone receptor, and PTEN gene (all P > 0.05). The expression of IR-A mRNA in EC patients with type 2 diabetes mellitus (DM) was significantly higher than that in patients without type 2 DM (P = 0.031), while there were no statistical correlation between the expression of IR mRNA and type 2 DM (P = 0.438). (2) The proliferation rates of the four kinds of EC cells was positively related with the IR-A expression ratio, with the most growth potential in Ishikawa, followed by HEC-1-A, KLE and RL95-2 cells. The overexpression of IR-A in RL95-2 (IR-A) cells showed a significant proliferation-promoting effect than that in control RL95-2 cells (P < 0.01).
Conclusion: There are two isoforms of IR-A and IR-B co-expressed in EC. The overexpression of IR-A may promote the proliferation of EC cells.