<b>Enhancement of Src Family Kinase Activity is Essential for p38 MAP Kinase-Mediated Dedifferentiation Signal of Parotid Acinar Cells </b>

Abstract

Decrease in saliva causes serious problems in clinical dentistry. There have been previous reports on tissue injuries of parotid glands inducing a dedifferentiation signal that causes the loss of function of acinar cells. Since both inhibitors for Src family kinase (SFK) and p38 MAP kinase (p38 MAPK) suppressed the dedifferentiation, SFK-p38 MAPK pathway was considered essential for the signaling. Even though Src and Yes were expressed in the parotid glands, the increase in phosphorylation level was not detected for conserved tyrosine residue in the kinase domain of Src or Yes that promotes kinase activity, following tissue injuries. In this study, the kinase activities were assayed by using the specific substrate for SFK to examine whether the enhancement of kinase activity of SFK was eventuated by tissue injuries. As a result, the activity of the total SFK was elevated after the cellular damage and was sustained for 2 h. To determine the activated SFK member, the SFK activity was examined by immunoprecipitation method with specific antibodies against each SFK member. Elevation of kinase activities of both Src and Yes was detected after cell damages. The elevation ratio of Src activity was higher than Yes, suggesting that the contribution of Src in the dedifferentiation signaling is higher.Diphenyleneiodonium, an NADPH oxidase inhibitor, suppressed the activation of SFK and p38 MAPK, and the expression of claudin-4, a dedifferentiation marker. These results suggest that the activation of SFK is induced by oxidative stresses and is essential for p38 MAPK-mediated dedifferentiation signaling.

Suppression of parotid acinar cell dysfunction by the free radical scavenger 3-methyl-1-phenyl-2-pyrazolin-5-one

“…MCI-186 treatment suppressed the phosphorylation of p38, which is mediated by Src activation, as shown previously (4). Generation of ROS may be involved in Src activation, as the NADPH oxidase inhibitor DPI suppresses the activation of both Src and p38 (5). However, the viability of cultured cells at 24 h after isolation was decreased in the presence of DPI (data not shown).…”

“…These results suggest that the Src-p38 signaling pathway plays a role in triggering cell dedifferentiation to ensure survival in response to cellular stress (4). Diphenyleneiodonium (DPI), nicotinamide adenine dinucleotide phosphate (NADP) oxidase inhibitor, suppresses activation of Src and p38 (5). Therefore, reactive oxygen species (ROS) may be generated during cell isolation, and these may activate Src.…”

Change in Expression Patterns of Micro RNAs in the Primary Culture of Parotid Acinar Cells

“…In addition, the expression levels of aquaporin-5, which is essential for water secretion, decreased during the culture (4). We found that the process of cell isolation from the glands triggered the stress signal mediated by Src and p38 MAP kinases (4,5).…”