In addition, differentiation reversal was highly specific since, at physiologically significant concentrations, closely related serine proteases did not cause neurite retraction. Prothrombin and thrombin also reversed morphological differentiation in the SK-N-SH neuroblastoma cell line and in heterogeneous cultures of cells from various regions in the human foetal brain. | The EMBO Journal pp. 2209 - 221 5, 1 989 Modulation of morphological differentiation of human neuroepithelial cells by serine proteases: independence from blood coagulation Roger ', Peter , Michael and Phillip Cancer Research Campaign Laboratories, Department of Cancer Studies, University of Birmingham, The Medical School, Birmingham B15 2TJ and 2Channel Diagnostics, Walmer, Kent, UK 'To whom correspondence should be addressed Communicated by We have previously shown that a serum protein, termed differentiation reversal factor (DRF), is responsible for neurite retraction in differentiated cultures of an adenovirus 12 (Adl2) transformed human retinoblast cell line. Data is presented here to show that DRF is identical to the serine protease prothrombin. Both proteins have been immunoprecipitated using an antibody raised against purified prothrombin and have been shown to hydrolyse a specific thrombin substrate only after activation by the snake venom ecarin. Following addition to Adl2 HER 10 cells, which had previously been differentiated by culture in the presence of 2 mM dibutyryl cAMP in serum-free medium, thrombin and prothrombin caused half-maximal retraction of neurites at concentrations of ng/ml and 20 ng/ml respectively. Interestingly, activation of prothrombin was shown to be unnecessary for biological activity. Using the inhibitor di-isopropylfluorophosphate (DIP), we have shown that abrogation of the proteolytic activity of thrombin also results in a loss ( > 2000 fold) of differentiation reversal activity. Thrombin and its zymogen both stinulated the mitosis of differentiated Adl2 HER 10 cells to a sinilar extent. In addition, differentiation reversal was highly specific since, at physiologically significant concentrations, closely related serine proteases did not cause neurite retraction. Prothrombin and thrombin also reversed morphological differentiation in the SK-N-SH neuroblastoma .
