As shown in Figure 4, E2-increased HBO1 protein expression was significantly suppressed by treatment with inhibitor of MEK1/2 (U0126) in T47 D (Figure 4A) and MCF-7 (Figure 4B) cells as analyzed by western blot. These results indicated that ERK1/2 signaling pathway was involved in the E2-induced HBO1 upregulation in breast cancer cells. Figure 4 E2 enhances HBO1 expression through ERK1/2 signaling pathways. (A) Serum-starved
T47 D cells were treated with E2 (10-8 M), or U0126 (10 uM) plus E2 (10-8 M) for 24 hours. Then equal amounts of protein (lysates) were subjected to SDS-PAGE. Western blot was performed using the Anti-phospho-ERK1/2 (Thr202/Tyr204), CP 868596 anti-HBO1 and anti-ERK1/2 antibodies. GAPDH was used as an internal control. (B) Serum-starved MCF-7 cells were treated with E2 (10-8 M), or U0126 (10 uM) plus E2 (10-8 M) for 24 hours. Western blot was performed as described in (A). Discussion HBO1 is a potential oncogene which maps to17q21.3, a region where frequent allelic gains are found in breast cancers Alectinib cost and this amplification is associated with a poor prognosis of clinical outcome [14–16]. Previous
studies demonstrated over-expression of HBO1 dramatically enhanced the anchorage-independent growth of both MCF7 and SKBR3 breast cancer cells while depletion of HBO1 reduced the rate of DNA synthesis, the amount of MCM complex bound MEK inhibitor to chromatin, and progression through S phase. HBO1 has also been shown to enhance transcription mediated by steroid receptors including ERα and PR . However, little is known about the role of HBO1 in breast cancer and the underlying molecular mechanism. In this study, we first investigated the HBO1 protein expression in large
numbers of tumor samples of primary breast cancer (n = 112) by IHC analysis, and showed that HBO1 was highly expressed in breast cancer (Table 1) and positively correlated with ERα (p < 0.001) and PR (p = 0.002). Moreover, HBO1 protein level correlated positively with histology grade in ER positive tumors (p = 0.016) rather than ERα negative tumors through statistical analysis. As a coactivator of the replication licensing factor Cdt1 , HBO1 belongs to one component of the Replication Initiation Proteins known as prereplicative complex (pre-RC) proteins. Several pre-RC proteins are over-expressed in cancer and serve as good tumor markers. And some of them, such as Cdc6 and Cdt1, are elevated by E2 treatment in breast cancer. To determine whether HBO1 was also affected by E2, quantitative real-time PCR and western blot were performed. The results suggested HBO1 was elevated after E2 treatment. Further study demonstrated the E2-induced HBO1 upregulation could be inhibited by ICI 182,780 as well as ERα siRNA.