Brefeldin A, a commonly used inhibitor of ER-to-Golgi apparatus transport, has been shown to inhibit transcytosis in dog kidney cells, which provided the first clues as to the nature of transcytosis regulation.[9] Transcytosis in dog kidney cells has also been shown be regulated at the apical membrane by Rab17,[10] as well as Rab11a and Rab25.[11] Further work on dog kidney cells has shown that a signaling cascade involving the phosphorylation of EGFR by Yes leading to the activation of Rab11FIP5 by MAPK1 upregulates transcytosis.[12] Transcytosis has been shown to be inhibited by the combination of progesterone and estradiol followed by activation mediated by prolactin in the rabbit mammary gland during pregnancy.[13] In the thyroid, follicular cell transcytosis is regulated positively by TSH [citation needed].