On the relationship between breast tumor kinase (Brk) and HaCaT cells differentiation

• Main Authors: Tsun-Cheng Wang, 王敦正
• Other Authors: Ruey-Hwa Chen
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/56532578294235024565

碩士 === 國立臺灣大學 === 分子醫學研究所 === 90 === Differentiation of epidermal keratinocytes is a complex process involving simultaneously turning on or turning off multiple biochemical reactions. Tyrosine phosphorylation is one of the well defined events during keratinocytes differentiation. Many protein tyrosine kinases have been found to play important roles. Breast tumor kinase (Brk), a non-receptor protein tyrosine kinase initially identified from metastatic breast tumor, exhibits dual functions both in tumorigenesis and differentiation. Based on a previous report that its mouse orthologue, Sik, is involved in keratinocyte differentiation, we focuses on Brk in human aspects. The results of histochemical staining of various cutaneous specimens and indirect immunofluorescence of cultured HaCaT cells demonstrated that Brk is expressed exclusively in suprabasal keratinocytes. The subcellular localization of Brk is both cytoplasmic and intranuclear. Although manipulating extracellular calcium concentration can regulate the differentiation of cultured human and mouse primary keratinocytes, we found that Brk is insensitive to calcium concentration in the culture medium. Using prolonged confluence of HaCaT cells as an in vitro keratinocytes differentiation model, we found both the mRNA and protein levels of Brk can be up-regulated, and that this regulation is serum-dependent. Under serum free conditions, the differentiation markers can still be up-regulated while the expression of Brk is suppressed, indicating both are not necessarily co-regulated. Preliminary data did not show significant variations in differentiation markers among the prototype cells and the stably transfected cells either with intact Brk cDNA or its kinase-dead mutant. A yet to be determined 70 kD band was found in the total cellular phosphotyrosine profile of Brk overexpressed cells. Further studies are needed to clarify mutual relationships between Brk and keratinocytes differentiation.