LAUSR

ERBB2 is a member of the EGFR growth factor receptor family and a primary target for anti-cancer treatment in patients diagnosed with breast cancer. ERBB2 targeting is known to cause cardiotoxicity, resulting in cardiac dilation while, less is understood about the underlying mechanisms. Studies have shown a direct co-relationship between beta2-adrenergic receptors (β2ARs) and ERBB2 in the cardiac hypertrophy wherein increased ERBB2 expression is associated with elevated β2ARs. Given the key role of β1ARs in cardiac function, we assessed potential cross-talk between ERBB2 and β1ARs. Towards this end, we have used a transgenic mouse model of cardiomyocyte-specific overexpression of microRNA-7 (miR-7 Tg) that abrogates ERBB2 expression in the adult cardiomyocytes and associated with cardiac dilation. Radio-ligand binding in miR-7 Tg hearts showed selective increase in β1AR density with no changes in the β2ARs. In contrast, cardiomyocyte-specific overexpression of ERBB2 results cardiac hypertrophy and is associated with significant increase in β2AR density with no changes in β1ARs. These observations show that ERBB2 expression may differentially regulate β1AR versus β2AR providing a unique role for ERBB2 in cardiac physiology. Further, ERBB2 expression is elevated in an age-dependent manner in C57BL6 mice that may account for hypertrophic response. Consistently, miR-7 Tg mice have age-dependent cardiac dilation consistent with the loss in the ERBB2 expression. To test for such a role, C57BL6 mice were administered vehicle, AG1875 (EGFR inhibitor) or AG825 (ERBB2 inhibitor) for two weeks to assess for changes in cardiac function. Administration of AG825 resulted significant cardiac dysfunction and dilation compared to AG1875 or vehicle controls, conferring the idea that inhibition of ERBB2 and not EGFR that mediates deleterious remodeling. Proteomic analysis showed dramatic differences in the associated proteins following AG825 compared to vehicle or AG1478 and our presentation will elucidate the results on how homeostatic ERBB2 signaling and expression is key for cardiac function and how chemotherapeutic inhibition of ERBB2 underlies deleterious pathways leading to cardiotoxicity.