The cyclin-dependent kinase inhibitors (CKIs) belong to a group of key cell cycle proteins that regulate important cancer drug targets such as the cyclin/CDK complexes. Gene defects in the INK4A/B CKI tumor suppressor locus are frequently associated with human cancers and we have previously identified similar defects in canine models. Many of the cancer-associated genetic alterations, known to play roles in mammary tumor development and progression, appear similar in humans and dogs. The objectives of this study were to characterize expression defects in the INK4 genes, and the encoded p16 family proteins, in spontaneous canine primary mammary tumors (CMT) as well as in canine malignant melanoma (CML) cell lines to further develop these models of spontaneous cancers. Gene expression profiles and characterization of p16 protein were performed by rtPCR assay and immunoblotting followed by an analysis of relevant sequences with bioinformatics. The INK4 gene family were expressed differentially and the genes encoding the tumor suppressor p16, p14, and p15 proteins were often identified as defective in CMT and CML cell lines. The altered expression profiles for INK4 locus encoded tumor suppressor genes was also confirmed by the identification of similar gene defects in primary canine mammary tumor biopsy specimens which were also comparable to defects found in human breast cancer. These data strongly suggest that defects identified in the INK4 locus in canine cell lines are lesions originating in spontaneous canine cancers and are not the product of selection in culture. These findings further validate canine tumor models for use in developing a clear understanding of the gene defects present and may help identify new therapeutic cancer treatments that restore these tumor suppressor pathways based on precision medicine in canine cancers.

细胞周期蛋白依赖性激酶抑制剂 (CKI) 属于一组关键细胞周期蛋白，可调节重要的癌症药物靶点，例如细胞周期蛋白/CDK 复合物。INK4A/B CKI 肿瘤抑制基因座中的基因缺陷经常与人类癌症相关，我们之前已经在犬模型中发现了类似的缺陷。许多与癌症相关的基因改变，已知在乳腺肿瘤的发展和进展中发挥作用，在人类和狗中看起来相似。本研究的目的是表征自发性犬原发性乳腺肿瘤 (CMT) 以及犬恶性黑色素瘤 (CML) 细胞系中 INK4 基因和编码的 p16 家族蛋白的表达缺陷，以进一步开发这些自发性乳腺癌模型。癌症。p16 蛋白的基因表达谱和表征通过 rtPCR 测定和免疫印迹进行，然后用生物信息学分析相关序列。INK4 基因家族差异表达，编码肿瘤抑制基因 p16、p14 和 p15 蛋白的基因通常在 CMT 和 CML 细胞系中被鉴定为有缺陷。INK4 基因座编码的肿瘤抑制基因的表达谱的改变也通过在原发性犬乳腺肿瘤活检标本中鉴定出类似的基因缺陷得到证实，这些缺陷也与人类乳腺癌中发现的缺陷相当。这些数据强烈表明，在犬细胞系中 INK4 基因座中鉴定的缺陷是起源于自发性犬癌的病变，而不是培养选择的产物。