Loss of Caveolin-3 Induces the Development of a Lactogenic Microenvironment

Here, we show that functional loss of a single gene is sufficient to confer constitutive milk protein production and protection against mammary tumor formation. Caveolin-3 (Cav-3), a muscle-specific caveolin-related gene, is highly expressed in striated and smooth muscle cells. We demonstrate that Cav-3 is also expressed in myoepithelial cells within the mammary gland. To determine if genetic ablation of Cav-3 expression affects adult mammary gland development, we next studied the phenotype(s) of Cav-3 (-/-) null mice. Interestingly, detailed analysis of Cav-3 (-/-) virgin mammary glands shows dramatic increases in ductal thickness, side-branching, and the development of extensive lobulo-alveolar hyperplasia, akin to the changes normally observed during pregnancy and lactation. Analysis by genome-wide expression profiling reveals the upregulation of gene transcripts associated with pregnancy/lactation, mammary stem cells, and human breast cancers, consistent with a constitutive lactogenic phenotype. The expression levels of three key transcriptional regulators of lactation, namely Elf5, Stat5a, and c-Myc are also significantly elevated. Experiments with pregnant mice directly show that Cav-3 (-/-) mice undergo precocious lactation. Finally, using orthotopic implantation of a transformed mammary cell line (known as Met-1), we demonstrate that virgin Cav-3 (-/-) mice are dramatically protected against mammary tumor formation. Interestingly, Cav-3 (+/-) mice also show similar protection, indicating that even reductions in Cav-3 levels are sufficient to render these mice resistant to tumorigenesis. Thus, Cav-3 (-/-) mice are a novel preclinical model to study the protective effects of a constitutive lactogenic microenviroment on mammary tumor onset and progression. Our current studies have broad implications for using the lactogenic micro-environment as a paradigm to discover new therapies for the prevention and/or treatment of human breast cancers. Most importantly, a lactation-based therapeutic strategy would provide a more natural and nontoxic approach to the development of novel anti-cancer therapies. All WT and Cav-3 knockout (KO) mice used in this study were in the FVB/N genetic background. 4-month old virgin female mice were utilized in a micro array study between 3 wildtype and 3 Caveolin-3 knock-out mammary glands.

本研究证实，单个基因的功能缺失足以使机体持续产生乳蛋白，并可预防乳腺肿瘤的发生。窖蛋白-3（Caveolin-3，Cav-3）是一种肌肉特异性的窖蛋白相关基因，在横纹肌和平滑肌细胞中呈高表达。本研究发现，Cav-3在乳腺的肌上皮细胞中同样存在表达。为明确Cav-3表达的基因敲除是否会影响成年乳腺发育，我们后续对Cav-3(-/-)纯合敲除小鼠的表型进行了研究。有趣的是，对未交配的Cav-3(-/-)小鼠乳腺的详细分析显示，其导管厚度、侧枝分支以及广泛的腺泡-小叶增生均显著增加，这与妊娠和泌乳期正常乳腺的变化相似。全基因组表达谱分析结果显示，与妊娠/泌乳、乳腺干细胞以及人类乳腺癌相关的基因转录本均出现上调，这与持续性泌乳表型的特征相符。泌乳过程中的三种关键转录调节因子——Elf5、Stat5a及c-Myc的表达水平同样显著升高。对妊娠小鼠的实验直接证实，Cav-3(-/-)小鼠会出现泌乳提前的现象。最后，通过将转化乳腺细胞系（命名为Met-1）进行原位移植的实验，我们证实未交配的Cav-3(-/-)小鼠可显著抵御乳腺肿瘤的发生。值得注意的是，Cav-3(+/-)杂合子小鼠同样表现出类似的肿瘤抵御能力，这表明即便仅降低Cav-3的表达水平，也足以使小鼠对肿瘤发生产生抗性。因此，Cav-3(-/-)小鼠是一种全新的临床前模型，可用于研究持续性泌乳微环境对乳腺肿瘤发生与进展的保护作用。本研究的成果具有广泛的应用前景，可将泌乳微环境作为研究范式，以开发用于人类乳腺癌预防和/或治疗的新型疗法。尤为重要的是，基于泌乳的治疗策略可为新型抗癌疗法的开发提供一种更天然、无毒的途径。本研究中使用的所有野生型（Wild Type, WT）及Cav-3敲除（Knockout, KO）小鼠均为FVB/N遗传背景。本研究的微阵列实验使用了4月龄未交配的雌性小鼠，分别取3只野生型小鼠与3只Cav-3敲除小鼠的乳腺组织进行检测。