The DNA primase polypeptide 1 (PRIM1) is responsible for synthesizing small RNA primers for Okazaki fragments generated during discontinuous DNA replication. PRIM1 mRNA expression levels in breast tumor samples were detected by real-time PCR analysis. Xenografted tumor model was established to study the carcinogenic role of PRIM1 and its potential therapeutic applications. The average PRIM1 mRNA (copy number × 10 /μg) expression was 4.7-fold higher in tumors than in normal tissue (*p = 0.005, n = 254). PRIM1 was detected preferentially at a higher level (>40-fold) in poorly differentiated tumor tissues (n = 46) compared with more highly differentiated tumors tissues (n = 10) (*p = 0.005). Poor overall survival rate was correlated to the estrogen receptor positive (ER+, n = 20) patients with higher PRIM1 expression when compare to the ER- (n = 10) patients (Chi Square test, p = 0.03). Stable expression of PRIM1-siRNA in the ER+ BT-474 cells-xenograft tumors significantly reduced tumor volume in SCID mice (*p = 0.005). The anti-tumoral effects of inotilone isolated from Phellinus linteus was tested and had significant effects on the inhibition of PRIM1 protein expression in ER+ breast cancer cells. In vivo study was performed by administering inotilone (10 mg/kg, twice a week for 6 weeks), which resulted in significantly reduced BT-474-xenografted tumor growth volume compared with control (n =5 per group, *p < 0.05). This study provides evidences for the prognostic effects of PRIM1 with poor overall survival rate in the ER+ patients and will be valuable to test for therapeutic purpose.
Breast cancer (BC) is the most common cancer affecting women worldwide and has been associated with active tobacco smoking. Low levels of nicotine (Nic) and 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK), have been detected in cases of second‐hand smoke (SHS). However, the correlation between SHS and BC risk remains controversial. In this study, we investigated whether the physiological SHS achievable dose of Nic and tobacco specific nitrosamine, NNK act together to induce breast carcinogenesis using an in vitro breast cell carcinogenesis model. Immortalized non‐tumorigenic breast epithelial cell line, HBL‐100 used for a time‐course assay, was exposed to very low levels of either Nic or NNK, or both. The time‐course assay consisted of 23 cycles of nitrosamines treatment. In each cycle, HBL‐100 cells were exposed to 1pM of Nic and/or 100 femtM of NNK for 48 hours. Cells were passaged every 3 days and harvested after 10, 15, and 23 cycles. Our results demonstrated that the tumorigenicity of HBL‐100, defined by soft agar colony forming, proliferation, migration and invasion abilities, was enhanced by co‐exposure to physiologically SHS achievable doses of Nic and NNK. In addition, α9‐nAChR signaling activation, which plays an important role in cellular proliferation and cell survival, was also observed. Importantly, an increase in stemness properties including the prevalence of CD44+/CD24− cells, increase Nanog expression and mammosphere‐forming ability were also observed. Our results indicate that chronic and long term exposure to environmental tobacco smoke, may induce breast cell carcinogenesis even at extremely low doses.
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