OR30-1 Cloning, Sequencing, and Characterization of Aromatase Interacting Partner in Breast (AIPB). A New Protein Regulating Estradiol Synthesis.

Abstract

Abstract Breast cancer is the most common invasive cancer in females worldwide and accounts for 16% of all female cancers, 22.9% of invasive cancers in women, and 18.2% of all cancer-related deaths worldwide. About 80% of these cancers, once established, depend on available estrogens (i.e., estradiol) to grow. The production of estrogens occurs via a catalytic process governed by the enzyme Aromatase. This process occurs primarily in the ovaries in pre-menopause, while in post-menopause, this occurs in peripheral tissues, including the breast. In patients whose cancers have specific hormone receptors, such as Estrogen Receptor positive (ER+), Progesterone Receptor positive (PR+), and Human Epidermal Growth Factor 2 Receptor positive (HER2+), these tumors can continue receiving nutrients and signals to grow, which provides targets for therapy. Although many of the currently available drugs for breast cancer seek to suppress this process and thus reduce available estrogens, they have numerous harmful side effects and have high rates of therapy failure due to the development of resistance. Therefore, new therapies and targets for this devastating disease are needed. We observed that breast tumors had increased estrogen production in postmenopausal women, leading us to question the cause of this increase. Further, the complete mechanism of aromatase action and the possibility of targetable cofactors remained previously unknown. Thus, we set out to identify the mechanism of Aromatase action to provide prognostic and therapeutic insight into this distressing disease. As Aromatase is an endoplasmic reticulum (ER) resident protein, we purified ER fractions from breast tissues, separated through 1D, and then each ten kDa fractions were further separated and analyzed through Mass-spectrometry to determine the cofactors associated with aromatase activity. We observed an 11 mer peptide LEVVVDQPMER, which on cloning resulted in a 207 amino acid protein not present in the database. This previously undiscovered protein is colocalized with Aromatase in the ER. We saw that knocking down its expression by siRNA in wild-type breast cells (MCF-12A) or tumorigenic MCF-7 or T47-D cells increased estradiol synthesis significantly without affecting aromatase expression. Further biochemical experiments showed that Aromatase and the 207 amino acid protein interacted directly without affecting the expression of other ER-resident proteins. Additionally, our experiments showed that the new protein is not hormonally stimulated or transcriptionally inhibited and thus, regulates the aromatase catalytic activity of estradiol synthesis. Therefore, we have termed this new protein "Aromatase Interacting Partner in Breast" (AIPB). Presentation: Tuesday, June 14, 2022 9:45 a.m. - 10:00 a.m.