A comparison of endocytic processes in untransfected and transfected Madin-Darby canine kidney cells expressing human growth hormone

The studies conducted herein included a comparison of endocytic processes of untransfected Madin-Darby canine kidney (MDCK) cells with those of transfected MDCK cells designated as, clone 3A. Cloned cells expressed great amounts of human growth hormone (hGH) and consequently contained amplified Golgi complexes. It was proposed that if the amplification of Golgi had led to greater vesicular trafficking from the Golgi apparatus to the the plasma membrane, then perhaps there was also a compensatory increase in the rate of endocytosis in clone 3A cells. The rates of horseradish peroxidase (HRP) arrival at the late endosome when internalized basolaterally in 3A cells were markedly increased over those of MDCK cells. In addition, because the rates of recycling and transcytosis from the early endosome were not increased in MDCK cells, the late endosomal compartment in 3A cells was considered to be enlarged which would be justified by the necessity of 3A cells to compensate for the over expression of hGH. Although there was no increase in acid hydrolase activity among the lysosomal enzymes tested, this does not rule out the possibility of increased degradation by lysosomal proteases among clone 3A cells.