Receptor-Mediated Endocytosis of CD34 on Hematopoietic Cells after Stimulation with the Monoclonal Antibody Anti-HPCA-1

Abstract

CD34 most probably acts as a receptor molecule on hematopoietic progenitor cells; however, its precise function remains to be elucidated. To track the intracellular pathway of CD34 after binding of a stimulatory antibody (anti-HPCA-1), immuno-electron microscopical analysis was performed on cells of normal bone marrow (NBMPC), acute leukemias, and the KG1a cell line. Before stimulation, CD34 was evenly distributed over the cell surface. After binding of the anti-HPCA-1, but not the anti-HPCA-2 antibody to CD34 and labeling with 30-nm immunogold, a rapid capping of CD34 and a subsequent internalization from the cell surface via clathrin-coated pits and coated vesicles was observed. The percentage of internalized CD34/immunogold complexes ranged from 8 to 80% in the NBMPC and the leukemic blasts, whereas KG1a cells showed an internalization rate of only 0.42%. Moreover, in the KG1a cells, the CD34/immunogold complexes were not associated with the coated pits. These differences in CD34 internalization did not correlate to the mRNA expression for the full-length or truncated CD34 assessed by isotype-specific real-time PCR. Taken together, evidence was found that CD34 is a surface receptor molecule that is modulated by receptor-mediated endocytosis. CD34 on KG1a cells appears to have a functional and/or structural defect, preventing modulation of this epitope.

Gene Expression Study of Monocytes/Macrophages during Early Foreign Body Reaction and Identification of Potential Precursors of Myofibroblasts

“…In the ASMA + cells, an intracytoplasmic CD34 staining could be observed, while there was no CD34 staining in the ASMA − cells. Internalization of the CD34 receptor has already been shown to exist by receptor-mediated endocytosis [34]. This intracytoplasmic CD34 staining in ASMA + cells shows that these myofibroblast-like cells originate from the CD34 + subpopulation within the CD68 + cell population.…”

Selective Migration of Subpopulations of Bone Marrow Cells along an SDF-1α and ATP Gradient

“…Therefore, migrated stem cells would no longer be detected as such by flow cytometric analysis. For CD117, CD34, and CD133, internalization in response to specific triggers has been described [ 39 – 41 ]. The triggers, however, vary conspicuously, and no reports of internalization of these markers through migration have yet been published.…”

mTert induction in p21-positive cells counteracts capillary rarefaction and pulmonary emphysema

“…Alternatively, since both cell types develop from bipotent progenitors (Gillich et al, 2020 ), another possibility is that p21-promoter dependent expression of mTert promotes the differentiation of the progenitors into aerocytes. Since we could not reveal the differences in the level of Cd34 mRNA among the four genotypes by scRNA-seq, in contrast to the CD34 immunostaining, we propose that the level of the CD34 surface protein could be regulated by receptor-mediated endocytosis (Krauter et al, 2001 ) independently of the Cd34 gene transcription.…”