Lysosomes, growth factor activity, and carcinogenic implications

The aim of this paper is to point out a body of literature which up to now has been largely ignored by investigators in the area of growth factors This paper will offer a response to the questions: Why is it that inhibition of endolysosomal proteases (by agents such as leupeptin, methylamine, etc.) or inhibition of endocytosis block the activities of all growth factors and carcinogens so far studied? What role therefore can endocytosis and endolysosomes (E/L) play in the signal transduction process? As will be detailed below, in many cases involving growth factors, inhibition of E/L proteases results in complete or very significant loss of growth factor activity. That is, treatment with inhibitors of E/L proteases (i.e., leupeptin, antipain methylamine, etc.) erases the normal activity of growth factors affecting systems of concern to immunologists, endocrinologists, and cardiologists. There are strong indications in the literature that suggest that in the nervous system (of obvious interest to neuroscientists) endocytosis plays a vital role in the induced proliferation of neurons as well (of interest to neurologists). This paper will explore the implications and offer an explanation for these findings. Thus this communication will travel from one growth factor to another in order to demonstrate the universality of the model offered in this paper.