ABCA1 and colorectal adenocarcinoma: In this regard, the LXR-α downregulator homocysteine significantly reduced ABCA1/Abca1 mRNA and ABCA1 protein expression in vitro in THP-1 macrophages as well as in vivo in macrophages from Apoe knock-out C57BL/6 mice.335 The cattle metabolite dipeptide phenylalanine-proline decreased ABCA1 mRNA and ABCA1 protein levels in human colorectal adenocarcinoma-derived CaCo-2 cells.436 The observed downregulation of LXRB mRNA could explain the negative impact on ABCA1 expression.