Apoptotic volume decrease, pH acidification and chloride channel activation during apoptosis requires CD45 expression in HPB-ALL T cells

Abstract

Mitochondrial-perturbating agents such as toxic coumponds induce apoptosis. We note that the loss of CD45 expression in the lymphoblastic leukemia cell line HPB-ALL (HPB45.0) leads to an inhibition of nuclear apoptosis. Our hypothesis is that the absence of CD45 disturbs protein function regulated by a proto-oncogene of the Src family playing a significant role in nuclear apoptosis. In this work we explore the importance of a chloride efflux on DNA fragmentation. The role of tyrosine kinase in the function and regulation of the chloride channels was determined. Our results showed a disturbance of ionic homeostasis in CD45 deficient lymphocytes (CD45-) in contrast to normal lymphocytes (CD45+). The phosphorylation levels of the chloride channels are considerably inhibited in CD45-, while the expression levels of these channels are similar in the two types of cells. A hypertonic medium inhibits DNA fragmentation in CD45+ while a hypotonic medium increases DNA fragmentation in CD45-. Thus CD45 plays a significant role in nuclear apoptosis by the regulation of the chloride channels responsible for ionic homeostasis of the cell essential for the DFF40 activation.

Involvement of tyrosine phosphatase CD45 in apoptosis

“…The authors suggested that CD45 might inhibit phosphatidylserine redistribution in response to various non-apoptotic signals [107] confirming a possible role for CD45 in the flip-flop process. We also showed that the phosphorylation levels of the chloride channels are considerably inhibited in CD45-cells [97], suggesting the loss of their activation, which is in agreement with the loss of volume and intracellular acidification that are controlled by chloride channels [109]. It is known that the inhibition of Cl-efflux inhibits DNA fragmentation [110].…”

“…Deregulation of ion transport in apoptotic cells leads to changes in intracellular ion levels and disrupts enzyme activity. Our results showed a disturbance of ionic homeostasis in CD45-deficient lymphocytes compared to normal lymphocytes [97]. CD45-deficient cells were shown to lose capacity to reduce their cellular volume and intracellular pH acidification after TBT exposure two processes required for DNA fragmentation [104,105].…”

“…In another study, we demonstrated that CD45 plays a significant role in nuclear apoptosis through the regulation of ionic homeostasis [97]. Deregulation of ion transport in apoptotic cells leads to changes in intracellular ion levels and disrupts enzyme activity.…”

“…We previously demonstrated that CD45 could regulate the apoptosis induced by mitochondrial perturbators such as tributyltin (TBT) and hydrogen peroxide (H 2 O 2 ) [97,98]. TBT is a biocide agent used in antifouling paints that provokes potent immunotoxic effects in mammals, characterized in vivo by thymic atrophy and reduction of peripheral lymphocytes, by an antiproliferative and apoptotic mechanism [99,100].…”

In vivo real-time imaging of the liver with confocal endomicroscopy permits visualization of the temporospatial patterns of hepatocyte apoptosis

“…Condensation of ribosomes has been found in apoptotic cells (32) and may explain the altered fluorescence intensity; however, such details could not be resolved in vivo. An altered pH has been described in cells undergoing apoptosis (6), and fluorescent agents such as fluorescein are known to show a pH-dependent fluorescence intensity (27). However, variation of pH from seven to eight in intact liver slices did not result in altered fluorescence, and not all cells becoming dark underwent apoptosis, although apoptosis was always preceded by darkening.…”