Di-leucine Motifs of NOK/STYK1 Affects Its Protein Expression and Distribution in HeLa Cells

Abstract: NOK/STYK1 is a structurally unique member in receptor tyrosine kinase family (RTKs)， which has strong ability to facilitate tumorigenesis and metastasis. It is also involved in cellular endocytosis. Analysis of NOK protein sequence revealed that there were several di-leucine motifs. Di-leucine motifs have been reported to play important roles in cellular endocytosis， vesicle trafficking， signaling sorting and so on. In the present study， a series of mutants of NOK di-leucine motifs were established and their protein expression and cellular distribution pattern were analyzed in HeLa cells. The results indicated that mutation in different NOK di-leucine motifs caused different change of NOK protein expression level. The protein expression level of NOKL220P mutant was higher than wild type NOK whereas NOKL237P was lower than wild type. As to the cellular distribution， some mutants altered the cellular distribution pattern of NOK protein， including the proportion of dot pattern (DP)-containing cells to aggregation pattern (AP)-containing cells as well as the localization， the size and the number of NOK aggregates. The mutants of NOKL203P， NOK237P and L299P significantly reduced the formation of NOK aggregates in cells. In addition to the above， overexpression of NOKL41 had more distinctive localization on nuclear envelop whereas overexpression of L220P had more distinctive localization on cytoplasma membrane. Taken together， di-leucine motifs of NOK mediate its protein expression level and cellular distribution. Therefore， this study provides some new insights into understanding the molecular mechanism underlying NOK’s facilitation to tuomrigensis and metastasis.

CSTR: 32200.14.cjcb.2015.10.0007