Exploring Interactions Between Retinoid and Vitamin D Signaling in Salivary Gland Homeostasis and Cancer

文摘:

Abstract: Basal cell derived salivary and breast cancers are correlated with poor patient prognosis, increased cancer reoccurrence and lack of definitive therapies 1. In both branching organs, cytokeratin 5-positive (K5+) basal cells contribute to ductal cells during normal development 2–4 and recent research has highlighted similarities in the K5+ basal cell origin of mammary and salivary squamous cells 5,6. In mammary tumors of basal origin, irradiation- resistant cancer stem cells (CSCs) demonstrate K5 positivity 1. Both Vitamin D and Vitamin A signaling pathways have been implicated in prevention of tumorigenesis 7,8. In the developing 9 salivary gland, we and others 10 have recently demonstrated that retinoic acid receptor (RAR) signaling contributes to expansion of K5+ basal cells, a phenomena conserved in the adult salivary gland 11. In both mammary 12 and salivary glands 13, CSCs display an upregulated level of ALDH, an aldehyde dehydrogenase that oxidizes Vitamin A to retinol, the precursor to retinoic acid and signaling through RARs. The relationship between RAR signaling and K5+ basal cells during tumorigenesis has yet to be explored. Work in the Welsh laboratory has shown that deletion of the Vitamin D receptor (VDR) in mice leads to increased cell proliferation and tumorigenesis in the breast 7 where VDR activity is linked to K5+ cell fate transition 4. In human population studies, low levels of Vitamin D are associated with increased cancer incidence and progression 14–16. In the submandibular salivary gland (SMG), progenitor cell populations are highly positive for VDR 17 and in humans, VDR localizes to epithelial cells 18; yet, Vitamin D signaling has not been specifically explored in the salivary gland. We will test the hypothesis that co- activating VDR and RAR signaling will reduce K5+ basal cell expansion and tumorigenesis in the SMG. In this proposal we will address the following questions: 1) What is the role of VDR signaling in K5+ basal cell expansion and differentiation in the SMG? 2) Does VDR signaling synergize with RARα signaling to negatively regulate K5+ basal cell expansion in the SMG? 3) Will loss of VDR signaling synergize with inhibition of RARα signaling to enhance K5+ tumorigenesis in the SMG? 4) Will activation of VDR and RARα signaling in K5- TdTomato-positive tumor cells using directed delivery of vitamin derivatives and small molecules decrease tumorigenic cell properties? To determine if RARα and VDR signaling synergize in negatively regulating the K5+ population in the SMG, in Aim 1 we will inhibit RARα signaling in a VDR knockout K5 reporter mouse and trace K5+ basal cell fate. In Aim 2, we will determine if VDR and RARα pathways synergize to regulate K5+ cell expansion in basal salivary tumors. This aim will be achieved with targeted pharmacological inhibition of RARα signaling in a VDR knockout K5 reporter mouse induced for tumorigenesis with DMBA. Additionally, we will determine if activation of VDR and RARα signaling in K5-TdTomato-positive tumor cells using small molecules and vitamin derivatives in 3D culture will affect cell division and motility.