• 8-Cl-Adenosine enhances 1,25-dihydroxyvitamin D3-induced growth inhibition without affecting 1,25-dihydroxyvitamin D3-stimulated differentiation of primary mouse epidermal keratinocytes.

      Bollag, Wendy B; Zhong, Xiaofeng; Josephson, Sarah; Department of Medicine; Department of Cellular Biology and Anatomy; Institute of Molecular Medicine and Genetics (2004-08-10)
      BACKGROUND: Epidermal keratinocytes continuously proliferate and differentiate to form the mechanical and water permeability barrier that makes terrestrial life possible. In certain skin diseases, these processes become dysregulated, resulting in abnormal barrier formation. In particular, skin diseases such as psoriasis, actinic keratosis and basal and squamous cell carcinomas are characterized by hyperproliferation and aberrant or absent differentiation of epidermal keratinocytes. We previously demonstrated that 8-Cl-adenosine (8-Cl-Ado) can induce keratinocyte growth arrest without inducing differentiation. RESULTS: To determine if this agent might be useful in treating hyperproliferative skin disorders, we investigated whether 8-Cl-Ado could enhance the ability of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], a known keratinocyte differentiating agent and a clinical treatment for psoriasis, to inhibit keratinocyte growth. We found that low concentrations of 8-Cl-Ado and 1,25(OH)2D3 appeared to act additively to reduce proliferation of primary mouse epidermal keratinocytes. However, another agent (transforming growth factor-beta) that triggers growth arrest without inducing differentiation also coincidentally inhibits differentiation elicited by other agents; inhibition of differentiation is suboptimal for treating skin disorders, as differentiation is often already reduced. Thus, we determined whether 8-Cl-Ado also decreased keratinocyte differentiation induced by 1,25(OH)2D3, as measured using the early and late differentiation markers, keratin 1 protein levels and transglutaminase activity, respectively. 8-Cl-Ado did not affect 1,25(OH)2D3-stimulated keratin 1 protein expression or transglutaminase activity. CONCLUSIONS: Our results suggest that 8-Cl-Ado might be useful in combination with differentiating agents for the treatment of hyperproliferative disorders of the skin.
    • Rab proteins in gastric parietal cells: evidence for the membrane recycling hypothesis.

      Calhoun, Benjamin C; Goldenring, J R; Department of Medicine (1997-07-08)
      The gastric parietal cell secretes large quantities of HCl into the lumen of the gastric gland in response to secretagogues such as histamine. In the membrane recycling hypothesis, this secretory activity requires the trafficking of the gastric H+/K(+)-ATPase to the cell surface from intracellular tubulovesicles. The Rab subclass of small GTP-binding proteins is thought to confer specificity to vesicle transport throughout the secretory pathway, and previous investigations established that Rab11 is highly expressed in gastric parietal cells. Recent discoveries in intra-Golgi transport and neuronal synaptic vesicle fusion have fortuitously converged on an evolutionarily conserved protein complex involved in vesicle docking and fusion. Recent results indicate that Rab11 is involved in the apical targeting of vesicles in parietal cells and other epithelial cells throughout the gastrointestinal tract. In support of the membrane recycling hypothesis, Rab co-segregates with H+/K(+)-ATPase in parietal cells. The presence of Rab11 on tubulovesicles supports a role for this Rab protein in recycling vesicle trafficking.