Mammary gland dual-expression construct containing prolactin and foreign DNAs can promote the expression of foreign proteins in mammary cells]

To investigate the feasibility in the promotion of the expression of foreign proteins, such as human lactinferrin (hLF) and thrombopoietin (TPO), in the transgenic animals-mammary gland bioreactor by bovine prolactin (bPRL), two types of mammary gland dual-expression vectors containing bPRL and foreign DNAs were constructed. In one type of vector, both foreign and bPRL DNAs were linked by internal ribosome entry site (IRES) which shared one goat 6.7 kb of beta-casein promoter; while in the other type of vector, the transcriptions of the foreign gene as well as bPRL were respectively directed by 6.7 kb goat beta-casein promoter and 2.0 kb of goat beta-casein promoter. After transfection of the vectors with lipofectin method, the expression of foreign proteins were measured by RT-PCR as well as ELISA assay. The results showed that bPRL could obviously promote the expression of foreign proteins (hLF and TPO) in cultured cells. The hLF expression level was increased from 12.6 microg/L to 18.4 microg/L and 37.2 microg/L in the COS-7 cells (African green monkey kidney cell) (P<0.05), and from 13.7 microg/L to 20.7 microg/L and 19.9 microg/L in the HC-11 cells (epithelial cell of mouse mammary gland) (P<0.05) by two vectors, respectively. TPO expression level was increased from 572 ng/L to 1340 ng/L in the COS-7 cell (P<0.05), and from 783 ng/L to 1040 ng/L in the HC-11 cell (P<0.05) by the vector which have two promoters. This work indicate that bovine prolactin can effectively increase the expression of foreign genes in mammal cells.