--- - |2 MiR‐24‐3p negatively modulates the expression of MEN1/menin in mammary epithelial cells by targeting the 3 'UTR of MEN1. MiR‐24‐3p plays regulatory role of cell proliferation and milk protein synthesis in mammary epithelial cells through cooperatively acting with menin. Abstract MiR‐24‐3p, a broadly conserved, small, noncoding RNA, is abundantly expressed in mammary tissue. However, its regulatory role in this tissue remains poorly understood. It was predicted that miR‐24‐3p targets the 3′ untranslated region (3′‐UTR) of multiple endocrine neoplasia type 1 (MEN1), an important regulatory factor in mammary tissue. The objective of this study was to investigate the function of miR‐24‐3p in mammary cells. Using a luciferase assay in mammary epithelial cells (MAC‐T), miR‐24‐3p was confirmed to target the 3′‐UTR of MEN1. Furthermore, miR‐24‐3p negatively regulated the expression of the MEN1 gene and its encoded protein, menin. miR‐24‐3p enhanced proliferation of MAC‐T by promoting G1/S phase progression. MiR‐24‐3p also regulated the expression of key factors involved in phosphatidylinositol‐3‐kinase/protein kinase B/mammalian target of rapamycin and Janus kinase/signal transducer and activators of transcription signaling pathways, therefore controlling milk protein synthesis in epithelial cells. Thus, miR‐24‐3p appears to act on MAC‐T by targeting MEN1. The expression of miR‐24‐3p was controlled by MEN1/menin, indicating a negative feedback loop between miR‐24‐3p and MEN1/menin. The negatively inhibited expression pattern of miR‐24‐3p and MEN1 was active in mammary tissues at different lactation stages. The feedback mechanism is a new concept to further understand the lactation cycle of mammary glands and can possibly to be manipulated to improve milk yield and quality. - 'Journal of Cellular Physiology, Volume 234, Issue 2, Page 1522-1533, February 2019. '