The angiogenins: an emerging family of ribonuclease related proteins with diverse cellular functions

Angiogenin is a member of the ribonuclease superfamily, which shows an ever expanding collection of molecules being identified and cloned. It was initially isolated from the conditioned medium of cultured tumour cells. Its angiogenic activity appears to be critical for the maintenance and support of tumour growth. Angiogenin also plays a role in a number of non-malignant vasculoproliferative pathological conditions. Along with other related molecules, it has been identified in a wide variety of somatic tissues in adult and embryonic stages of vertebrate development. This suggests that angiogenin and related molecules are likely to play a vital role in normal physiology. Angiogenin is detectable in serum and to date has been implicated as a mitogen for vascular endothelial cells, an immune modulator with suppressive effects on polymorphonuclear leukocytes, an activator of certain protease cascades such as matrix metalloproteases and plasminogen-activated plasmin pathways, as well as an adhesion molecule. However, the role of the angiogenin family in both normal and abnormal physiology and in development will only fully be realised by genetic approaches involving gene deletion.