EXPRESSION OF CYP1B1 BUT NOT CYP1A1 BY PRIMARY CULTURED HUMAN MAMMARYSTROMAL FIBROBLASTS CONSTITUTIVELY AND IN RESPONSE TO DIOXIN EXPOSURE- ROLE OF THE AH RECEPTOR

The expression of CYP1B1 in human mammary fibroblasts (HMFs) was chara cterized as a potential modulator of their individual function as well as effects on adjacent mammary epithelia, We have used these characte ristics to explore the diversity of fibroblast cells isolated from red uction mammoplasty patients and from different breast locations in bre ast cancer patients (tumors, peripheral to tumor and skin). These para meters have also been used to examine differences between two donors, The results have shown that while none of these HMFs expressed a detec table CYP1A1 protein basally or in response to TCDD, they all expresse d CYP1B1 constitutively at similar levels (0.5-0.9 pmol/mg microsomal proteins) and they were induced by TCDD (up to 5-fold) consistent with mediation by the Ah receptor (AhR), DMBA metabolism by HMFs exhibited high proportions of 5,6-, 10,11- and 3,4-dihydrodiols, a profile that is typical of human CYP1B1 regioselectivity, RT-PCR followed by South ern blot analyses demonstrated that CYP1B1 mRNA expression in HMFs par allels levels of respective microsomal proteins. The AhR is expressed in these HMFs as two cytosolic forms (similar to 106 and 104 kDa) and a substantial proportion of the 104 kDa form was localized to the nucl eus even prior to TCDD treatment. In all HMFs isolated directly from c ollagenase digested breast tissues the AhR is expressed at levels 10-f old lower than in breast epithelial cells, However, HMFs that were iso lated after serial passaging of mammary epithelial cultures had shown much higher levels of the AhR expression and more dramatic TCDD-induce d down-regulation (>80% in 24 h) associated with more efficient nuclea r translocation. These differences suggested the presence of two funct ionally distinct subtypes of HMFs: interstitial stromal fibroblasts th at are readily released by collagenase digestion of breast tissues, an d lobular stromal fibroblasts which are more tightly associated with t he breast epithelia.