Análisis de la coexpresión de HER2/GRB7 y su asociación con variables clinicopatológicas en un grupo de mujeres colombianas con diagnóstico de cáncer de mama invasivo / Analysis of HER2/GRB7 co-expression and its association with clinicopathological variables in a group of Colombian women diagnosed with invasive breast cancer

Objetivo. Analizar las diferencias en la presentación de variables clínico-patológicas, de acuerdo con la expresión proteica de GRB7, en tumores HER2 positivos en mujeres colombianas con cáncer de mama invasivo, diagnosticado entre los años 2013 y 2015 en el Instituto Nacional de Cancerología E.S.E (INC). Métodos. Se incluyeron 158 pacientes con diagnóstico confirmado de cáncer de mama ductal invasivo. Se evaluó la expresión de los receptores hormonales (receptor de estrógeno (RE) y de progesterona (RP)), HER2, Ki67 y GRB7, mediante inmunohistoquímica (IHQ), y a partir de estos, se clasificaron los tumores en subtipos intrínsecos. Los análisis estadísticos incluyeron las pruebas de Chi-cuadrado/test exacto de Fisher para las variables categóricas, y la prueba U Mann Whitney/ Kruskal Wallis para las variables cuantitativas. Se evaluó la supervivencia global (SG) y libre de enfermedad (SLR) según la coexpresión de HER2/GRB7 usando el método de Kaplan-Meier y el test de log-rank. Resultados. La expresión de GRB7 se observó exclusivamente en tumores HER2-positivos (luminal B/HER2+ y HER2-enriquecidos: p<0,001). Los casos HER2+/GRB7+ mostraron una mayor expresión de Ki67 (40% vs. 27,5%, p=0,029), pero una tendencia a presentar un menor tamaño tumoral (30 mm vs. 51 mm, p=0,097), comparado con los tumores HER2+/GRB7-. No obstante, no se observaron diferencias en la supervivencia según la coexpresión de HER2/GRB7 (SG: p=0,6; SLR: p=0,07). Conclusiones. En nuestra muestra de estudio, la expresión de GRB7 en tumores HER2+ no se asoció con características clínico-patológicas de pronóstico desfavorable.

Objective: To analyze differences in the presentation of clinicopathological variables according to GRB7 protein expression in HER2-positive tumors in Colombian patients with invasive ductal breast carcinomas diagnosed between 2013 and 2015 at the Instituto Nacional de Cancerología (Bogotá, Colombia).Methods: A total of 158 breast cancer patients were included with a confirmed diagnosis of invasive ductal carcinoma. A single pathologist evaluated the protein expression of hormone receptors (estrogen (ER) and progesterone receptor (PR)), HER2, Ki67, and GRB7 by immunohistochemistry (IHC). The chi-square and Fisher's exact tests were used to assess differences between categorical variables, as well as the Mann-Whitney/Kruskal-Wallis U test for numerical variables. Overall (OS) and disease-free (DFS) survival were evaluated according to HER2/GRB7 co-expression using the Kaplan-Meier method and log-rank test.Results:GRB7 expression was observed exclusively in HER2-positive tumors (luminal B/HER2+ and HER2-enriched: p<0.001). HER2+/GRB7+ cases showed higher Ki67 expression (40% vs. 27.5%, p=0.029) and a tendency to present a smaller tumor (30 mm vs. 51 mm, p=0.097) compared to HER2+/GRB7- tumors. However, no differences in OS or DFS were observed by HER2/GRB7 co-expression (OS: p=0.6; DFS: p=0.07).Conclusions:Our results in Colombian patients indicate that GRB7 expression in HER2-positive breast tumors is not associated with unfavorable clinicopathological features.

Conservation and divergence of Grb7 family of Ras-binding domains

Ras proteins are signal-transducing GTPases that cycle between inactive GDP-bound and active GTP-bound forms. Ras is a prolific signaling molecule interacting with a spectrum of effector molecules and acting through more than one signaling pathway. The Ras-effector proteins contain a Ras-associating (RA) domain through which these associate with Ras in a GTP-dependent manner. The RA domain is highly conserved among the members of the growth factor receptor-bound (Grb) 7 family of proteins which includes Grb7, Grb10 and Grb14. Our laboratory has reported an unusual observation that RA domain of Grb14 binds to the C-terminal nucleotide binding site of cyclic nucleotide gated channel (CTRCNGA1) and inhibits the channel activity. Molecular modeling of the CTR-CNGA1 displays 50%-70% tertiary structural similarity towards Ras proteins. We named this region as Ras-like domain (RLD). The interaction between RA-Grb14 and RLD-CNGA1 is mediated through a simple protein-protein interaction temporally and spatially regulated by light and cGMP. It is interesting to note that Grb14 binds to GTPase-mutant Rab5, a Ras-related small GTPase whereas Grb10 binds only to GTP-bound form of active Rab5 but not to GTPase-defective mutant Rab5. These results suggest that Grb14 might have been evolved later in the evolution that binds to both Ras and nucleotide binding proteins such as CNGA1. Our studies also suggest that eukaryotic CNG channels could be evolved through a gene fusion between prokaryotic ion channels and cyclic nucleotide binding proteins, both of which might have undergone several sequence variations for functional adaptation during evolution.