Christenson Jessica L, Kane Susan E
Department of Cancer Biology, Beckman Research Institute at City of Hope, 1500 E, Duarte Road, Duarte, CA 91010, USA.
Mol Cancer. 2014 Aug 15;13:192. doi: 10.1186/1476-4598-13-192.
Darpp-32 and t-Darpp are expressed in several forms of breast cancer. Both are transcribed from the gene PPP1R1B via alternative promoters. In humans, Darpp-32 is expressed in both normal and malignant breast tissue, whereas t-Darpp has only been found in malignant breast tissue. The exact biological functions of these proteins in the breast are not known. Although Darpp-32 is a well known regulator of neurotransmission, its role in other tissues and in cancer is less well understood. t-Darpp is known to increase cellular growth, inhibit apoptosis and contribute to acquired drug resistance. The use of transgenic mouse mammary tumor models to study Darpp-32 and t-Darpp in breast cancer in vivo has been limited by a lack of knowledge regarding t-Darpp expression in mice, in both normal and malignant tissue.
We used RT-PCR and Western analysis to investigate Darpp-32 and t-Darpp levels in normal and malignant mouse mammary tissue. To determine if Darpp-32 and t-Darpp play a direct role in mammary tumor development, Ppp1r1b gene knockout mice and wild-type mice were crossed with a mouse mammary tumor model. Tumor growth and metastasis were examined. Differences between groups were determined by the two-tailed Student's t-test.
We found that Darpp-32 was expressed in normal mouse mammary tissue and in some breast tumors, whereas t-Darpp was found exclusively in tumors, with t-Darpp usually expressed at equal or higher levels than Darpp-32. Ppp1r1b knockout in MMTV-PyMT transgenic tumor mice resulted in a decrease in tumor growth.
The shift in expression from Darpp-32 to t-Darpp during mouse mammary tumorigenesis is reminiscent of the expression patterns observed in humans and is consistent with a role for t-Darpp in promoting cell growth and Darpp-32 in inhibiting cell growth. Decreased tumor growth in Ppp1r1b knockout mice also suggests that t-Darpp plays a direct role, predominant to Darpp-32, in mammary tumor development. These results indicate that transgenic mouse mammary tumor models might be valuable tools for future investigation of Darpp-32 and t-Darpp in breast cancer.
在多种乳腺癌中均有达普-32（Darpp-32）和截短型达普-32（t-Darpp）表达。二者均通过可变启动子由PPP1R1B基因转录而来。在人类中，达普-32在正常乳腺组织和恶性乳腺组织中均有表达，而截短型达普-32仅在恶性乳腺组织中被发现。这些蛋白在乳腺中的具体生物学功能尚不清楚。尽管达普-32是一种知名的神经传递调节因子，但其在其他组织及癌症中的作用却鲜为人知。已知截短型达普-32可促进细胞生长、抑制细胞凋亡并导致获得性耐药。由于缺乏关于截短型达普-32在正常和恶性组织中的小鼠表达情况的了解，利用转基因小鼠乳腺肿瘤模型在体内研究达普-32和截短型达普-32在乳腺癌中的作用受到了限制。
我们运用逆转录聚合酶链反应（RT-PCR）和蛋白质免疫印迹分析来研究正常和恶性小鼠乳腺组织中达普-32和截短型达普-32的水平。为了确定达普-32和截短型达普-32在乳腺肿瘤发生中是否发挥直接作用，将Ppp1r1b基因敲除小鼠和野生型小鼠与一种小鼠乳腺肿瘤模型进行杂交。对肿瘤生长和转移情况进行检测。通过双侧学生t检验确定组间差异。
我们发现达普-32在正常小鼠乳腺组织及部分乳腺肿瘤中表达，而截短型达普-32仅在肿瘤中被发现，且截短型达普-32的表达水平通常等于或高于达普-32。在MMTV-PyMT转基因肿瘤小鼠中敲除Ppp1r1b会导致肿瘤生长减缓。
在小鼠乳腺肿瘤发生过程中，从达普-32到截短型达普-32的表达转变类似于在人类中观察到的表达模式，并且与截短型达普-32促进细胞生长以及达普-32抑制细胞生长的作用相一致。Ppp1r1b基因敲除小鼠中肿瘤生长减缓也表明，截短型达普-32在乳腺肿瘤发生中发挥着直接作用，且作用强于达普-32。这些结果表明，转基因小鼠乳腺肿瘤模型可能是未来研究达普-32和截短型达普-32在乳腺癌中作用的有价值工具。
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