In vivo expression and characteristics of novel α-d-mannose-rich glycoprotein markers of apoptotic cells

We recently established that an increased expression of α-d-mannose (Man)- and β-d-galactose-rich plasma membrane glycoproteins (GPs) is characteristic for apoptotic cells in vitro [Bilyy, R.O., Stoika, R.S., 2003. Lectinocytochemical detection of apoptotic murine leukemia L1210 cells. Cytometry 56A, 89-95]. It was independent of cell line or apoptosis-inducing agent, and can therefore be considered as a selective marker for identification and isolation of apoptotic cells [Bilyy, R.O., Antonyuk, V.O., Stoika, R.S., 2004. Cytochemical study of role of alpha-d-mannose- and beta-d-galactose-containing glycoproteins in apoptosis. J. Mol. Histol. 35, 829-838]. The main goals of the present study were: (1) to determine whether an increased expression of specific GPs also takes place after apoptosis induction in vivo; and (2) to identify additional characteristics of the membrane GP markers of the apoptotic cells. To reach these goals, we studied the expression of α-Man-rich membrane GPs in murine leukemia L1210 cells inoculated into abdominal cavities of mice which were then subjected to the action of apoptosis inducer doxorubicin. Another experimental model used in the present work was splenocytes obtained from mice treated with dexamethasone. Lectin-affinity chromatography and PAGE electrophoresis, or PAGE electrophoresis and lectinoblot analysis were applied for isolation of plasma membrane GPs (34 kDa, and high MW of ∼600 and 800 kDa) whose expressions were increased during apoptosis. Triton X-114 treatment of cell membrane samples showed that the apoptotic cell-specific GPs were localized in the peripheral and integral compartments of plasma membrane. Apoptosis in vitro and in vivo was accompanied by an increased expression of the same GP, identified by MALDI-TOF MS analysis as the microtubule-actin cross-linking factor 1. Other GPs, whose expressions were also increased at apoptosis, were similarly identified as G-protein β-subunit like (Acc# BAA06185.1) and dystonin isoform β.