Protein Kinase D3 as a Novel Biomarker for Triple-negative Breast Cancer

描述(申请人提供)：三阴性乳腺癌(TNBC)，以缺乏雌激素受体(ER)、孕激素受体(PR)和HER2的乳腺肿瘤为特征，占所有乳腺癌的15%-20%。TNBC主要由基底细胞样分子亚型组成，具有明显的临床和病理特征。由于TNBC的侵袭性行为和总体存活率较低，因此它是一个重要的临床挑战；而且TNBC患者复发和死亡的风险很高。目前，缺乏针对TNBC的靶向治疗，使得化疗成为治疗的主要手段。因此，需要确定新的TNBC危险生物标记物，以防止疾病复发，并改善对TNBC患者的治疗和护理。在这项建议中，我们试图确定丝氨酸/苏氨酸蛋白激酶D3(PKD3)是否为一种新的TNBC生物标志物。PKD家族包括PKD1、PKD2和PKD3。我们最近发现，PKD2和PKD3是乳腺癌细胞中表达的两种主要的PKD亚型。与PKD2不同，PKD3在不同乳腺癌细胞系中的表达有所不同。我们发现PKD3在致瘤的TNBC细胞系(HCC1806和MDA-MB468)和稳定表达表皮生长因子受体(EGFR)的T47D乳腺癌细胞中高表达。相反，在ER阳性和HER2过表达的乳腺癌细胞系中，PKD3蛋白水平较低。通过使用PKD异构体特异性siRNAs，我们已经确定PKD3是在致瘤的HCC1806 TNBC细胞中介导PKD信号转导和细胞增殖的重要异构体。我们进一步表明，与过表达HER2的低PKD3乳腺癌细胞相比，高水平表达PKD3的乳腺癌细胞对PKD抑制剂的作用更大。根据这些发现，我们推测PKD3可能是乳腺癌，尤其是侵袭性TNBC的重要生长调节因子和风险生物标记物。我们将通过以下两个特定的目的来验证这一假说：目的1)确定PKD3在乳腺肿瘤中的表达，并探讨其表达与乳腺癌亚型和肿瘤恶性程度的关系；目的2)确定PKD3在体内TNBC生长和信号转导中的作用。我们期望这一建议将提供有价值的直接证据来评估侵袭性的TNBC是否比其他乳腺癌亚型表达更多的PKD3，以及PKD3是否是体内TNBC的关键生长调节因子。这些研究可能导致发现PKD3可能是一种新的TNBC的危险生物标志物。

DESCRIPTION (provided by applicant): Triple-negative breast cancer (TNBC), characterized by breast tumors lacking estrogen receptor (ER), progesterone receptor (PR) and HER2, comprises 15-20% of all breast cancers. TNBC mostly comprises the basal-like molecular subtype of breast cancer and has distinct clinical and pathologic features. TNBC represents an important clinical challenge because of its aggressive behavior and poor overall survival; and patients with TNBC have a high risk of relapse and death. Currently, targeted therapies for TNBC are lacking, leaving chemotherapy as the mainstay of treatment. Hence identification of new risk biomarkers for TNBC is needed to prevent the disease relapse and to improve treatment and care for patients with TNBC. In this proposal, we seek to determine whether the serine/threonine protein kinase D3 (PKD3) is a novel biomarker for TNBC. PKD family kinases include PKD1, PKD2 and PKD3. We have recently shown that PKD2 and PKD3 are two major PKD isoforms expressed in breast cancer cells. Unlike PKD2, PKD3 expression varied among breast cancer cell lines. We found that PKD3 was highly expressed in tumorigenic TNBC cell lines (HCC1806 and MDA-MB468) and in T47D breast cancer cells stably expressing epidermal growth factor receptor (EGFR). In contrast, PKD3 protein level was low in ER-positive and HER2-overexpressing breast cancer cell lines. By using PKD isoform-specific siRNAs, we have identified PKD3 as an important isoform mediating PKD signal transduction and cell proliferation in tumorigenic HCC1806 TNBC cells. We further showed that breast cancer cells expressing a high level of PKD3 were more responsible to PKD inhibitors compared with HER2- overexpressing breast cancer cells that have a low PKD3 level. On the basis of these findings, we hypothesize that PKD3 may be an important growth regulator and risk biomarker for breast cancer, especially for aggressive TNBC. We will test this hypothesis with following two Specific Aims: Aim 1) To determine the expression of PKD3 in breast tumors and correlate its expression with breast cancer subtypes and tumor malignancy; Aim 2) To determine the role of PKD3 in the growth and signaling of TNBC in vivo. We anticipate that this proposal will provide valuable direct evidence to assess whether the aggressive TNBC expresses more PKD3 compared with other breast cancer subtypes and whether PKD3 is a critical growth regulator of TNBC in vivo. These studies may lead to a finding that PKD3 could be a novel risk biomarker for TNBC.