17q21.33

BP1,DLX7,DLX8,DLX9,OFC15

Breast cancer

BP1 is activated in about 80% of invasive ductal breast (IDC) tumors. Aberrant expression of BP1 was shown by semi-quantitative RT-PCR, where 80% of tumors were BP1 positive, and by immunostaining, where 81% of tumors were BP1 positive, a remarkable agreement between mRNA and protein expression (Fu et al., 2003; Man et al., 2005). Surprisingly, 89% of the tumors of African American women (AAW) were BP1 positive, compared with 57% of the tumors of Caucasian women (p=0.04). In addition, 100% of ER negative tumors were BP1 positive, compared with 73% of ER positive (p=0.03). Both tumors of AAW and ER negative tumors are associated with aggressiveness. A group in China quantitated BP1 mRNA in the tumors of 142 Chinese women, discovering that 65% of their tumors were BP1 positive, and confirming an association between high BP1 mRNA expression and ER negative tumors (Yu et al., 2008b). Inflammatory breast cancer (IBC) is an extremely aggressive breast cancer, with approximately half the survival seen in IDC; 100% of the forty-six cases of IBC we examined were highly BP1 immunoreactive, suggesting an association between aggressiveness, frequency of BP1 positivity, and BP1 protein (pBP1) staining intensity (Man et al., 2009).
pBP1 expression correlates with breast cancer progression. The frequency of pBP1 positivity, distribution and intensity of BP1 expression all increased with the progression of tumor development from 0% (normal) to 21% in hyperplasia, 46% in ductal carcinoma in situ, and 81% in IDC (p

Leukemia

We examined BP1 in the bone marrow of leukemia patients by semi-quantitative RT-PCR, finding that BP1 was activated in 63% of acute myeloid leukemias (AML), including 81% of pediatric and 47% of adult patients with AML, in 32% of T-cell acute lymphocytic leukemias (ALL) but not in the pre-B ALL cases (Haga et al., 2000). Expression of BP1 occurred in primitive leukemia cells and in CD34 positive progenitors. In the same study we examined expression of DLX4 and DLX7 by designing primers specific for each isoform. Interestingly, the three isoforms were frequently co-expressed in the same cases. Next we compared the growth-inhibitory and cyto-differentiating activities of all-trans retinoic acid (ATRA) in two acute promyelocytic leukemia (APL) cells lines, NB4 (ATRA-responsive) and R4 (ATRA-resistant) cells relative to BP1 levels (Awwad et al., 2008). NB4 cells and R4 cells both expressed BP1; BP1 was repressed after ATRA treatment of NB4 cells but not R4 cells. In NB4 cells engineered to overexpress BP1, proliferation was no longer inhibited and differentiation was reduced two- to three-fold. In patients, BP1 levels were increased in all pre-treatment APL patients tested, while BP1 expression was decreased in 91% of patients after combined ATRA and chemotherapy treatment. Two patients underwent disease relapse during follow up; one patient exhibited a 42-fold increase in BP1 expression, while the other showed no change. This suggests BP1 may be part of a pathway involved in resistance to therapy.

Prostate cancer

Prostate cancer, another hormone dependent solid tumor, was examined for activation of BP1 (Schwartz et al., 2008). Significant BP1 immunoreactivity was identified in 70% of prostatic tumors, whether the analysis was performed on tissue sections (50 cases) or tissue microarray platforms (123 cases). We also observed low BP1 immunostaining in 42% of hyperplastic cells, similar to the 46% BP1 positivity in hyperplastic breast cells. Compared to normal and hyperplastic tissues, the malignant tissues consistently showed the highest number of BP1 positive cells and the highest intensity of BP1 immunostaining, similar to our observations in breast. In tissue sections, twelve cases with paired carcinoma and prostatic intraepithelial neoplasia (PIN) showed agreement, both components exhibiting strong immunoreactivity. Tumor proliferation, assayed with Ki67 immunostaining, was higher in cancer cells that were BP1 positive relative to those that were BP1 negative, in agreement with the data in breast cancer cells. These findings suggest that BP1 is an important upstream factor in the carcinogenic pathway of prostate cancer and that the expression of BP1 may reflect or directly contribute to tumor progression and/or invasion.

Non-small cell lung cancer (NSCLC)

An interesting study by Yu et al. (2008a) demonstrated that high BP1 mRNA levels occur in NSCLC tumors, compared with adjacent normal cells or normal lung samples. High mRNA levels are associated with stage III tumors, lower disease free survival (DFS) and lower overall survival. In fact, high BP1 mRNA is an independent predictor of DFS.