Abstract

Resistance of tumor cells to retinoic acid (RA), a promising therapeutic agent, is the major factor limiting the use of RA in clinical practice. The mechanisms of resistance to RA are still poorly understood. Cellular Retinoic Acid Binding Proteins, CRABP1 and CRABP2, are essential mediators of RA signaling, but role of the two CRABP homologs in regulating cellular sensitivity to RA has not been well studied. In addition, the effects of CRABP1 and CRABP2 on cell proliferation have not been compared. Here, using a broad panel of breast cancer cell lines with different levels of RA sensitivity/resistance, we show for the first time that in the RA-sensitive cells, CRABP1 expression is restricted by methylation, and protein levels are highly variable. In the moderately-RA-resistant cell lines, high level of CRABP1 is observed both at the mRNA and protein levels, unchanged by inhibition of DNA methylation. The cell lines with maximum resistance to RA are characterized by complete repression of CRABP1 expression realized at transcriptional and posttranscriptional levels, and exogenous expression of each of the CRABP homologs has no effect on the studied characteristics. CRABP1 and CRABP2 proteins have opposing effects on proliferation and sensitivity to RA. In particular, CRABP1 stimulates and CRABP2 reduces proliferation and resistance to RA in the initially RA-sensitive cells, while in the more resistant cells the role of each homolog in both of these parameters is reversed. Overall, we have shown for the first time that CRABP proteins exert different effects on the growth and sensitivity to RA of breast cancer cells (stimulation, suppression, or no effect) depending on the baseline level of RA-sensitivity, with the effects of CRABP1 and CRABP2 homologs on the studied properties always being opposite.

中文翻译：

---

CRABP1 和 CRABP2 同源物对乳腺癌细胞增殖及其对视黄酸敏感性的相反作用

摘要

肿瘤细胞对视黄酸（RA）这种有前景的治疗药物的耐药性是限制 RA 在临床实践中使用的主要因素。对 RA 的耐药机制仍知之甚少。细胞视黄酸结合蛋白 CRABP1 和 CRABP2 是 RA 信号传导的重要介质，但这两种 CRABP 同源物在调节细胞对 RA 敏感性中的作用尚未得到充分研究。此外，CRABP1和CRABP2对细胞增殖的影响尚未进行比较。在这里，我们使用具有不同 RA 敏感性/耐药性水平的广泛乳腺癌细胞系，首次证明在 RA 敏感性细胞中，CRABP1 表达受到甲基化的限制，并且蛋白质水平高度可变。在中度 RA 抗性细胞系中，在 mRNA 和蛋白质水平上均观察到高水平的 CRABP1，并且通过抑制 DNA 甲基化而保持不变。对 RA 具有最大抵抗力的细胞系的特征是在转录和转录后水平上实现 CRABP1 表达的完全抑制，并且每种 CRABP 同源物的外源表达对所研究的特征没有影响。CRABP1 和 CRABP2 蛋白对增殖和对 RA 的敏感性具有相反的作用。特别是，在最初对 RA 敏感的细胞中，CRABP1 刺激增殖，CRABP2 降低增殖和对 RA 的耐药性，而在耐药性更强的细胞中，每个同源物在这两个参数中的作用是相反的。总体而言，我们首次证明 CRABP 蛋白对乳腺癌细胞的生长和对 RA 的敏感性发挥不同的影响（刺激、抑制或无影响），具体取决于 RA 敏感性的基线水平，其中 CRABP1 的影响和CRABP2同系物在所研究的特性上总是相反的。