Roles Of Pi3-kinase And Pdk-1 in Rod Photoreceptor Differentiation
Open Access
- Author:
- Xing, Tiaosi
- Graduate Program:
- Anatomy
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 19, 2013
- Committee Members:
- Colin James Barnstable, Thesis Advisor/Co-Advisor
- Keywords:
- PDK-1
photoreceptor
retina development
PI3kinase
P85
p55 - Abstract:
- ABSTRACT The phosphoinositide 3-kinase (PI3-kinase) pathway regulates cell growth, survival, differentiation and proliferation. In response to insulin growth factor (IGF-1), PI3-kinase phosphorylates PIP2 to PIP3. Generation of PIP3 allows the activation of downstream effector proteins. Previous experiments suggested that the PI3-kinase class IA/PKCs/STAT3 pathway was linked to rod photoreceptor differentiation. Activation and inhibition of PI3-kinase class IA increased the number of rods after four days explant culture of postnatal day1 mouse retinas. Therefore, it was hypothesized that throughout retinal development there is a change in the expression of regulatory subunits of PI3-kinases family. Presence of PI3-kinase class IA regulatory subunits was examined in different ages of mouse retinas. It was found that although p85α, p55α and p55γ were present in mouse retinas, only tyrosine phosphorylation of p55α was detected in the retinas after postnatal day 5. These results suggest that p55α is the essential subunit controlling PI3-kinase class IA activity. 3-phosphoinositide-dependent protein kinase-1 (PDK-1) was identified as one of the downstream of PI3-kinase. It is a protein serine and threonine kinase required for protein kinase B (Akt) activation in many tissues. It is also a crucial activator of multiple protein kinases, including p70 ribosomal S6-kinase (p70S6K1), protein kinase isoforms (PKCs), and serum and glucocorticoid-inducible kinase (SGK). We also investigated whether PDK-1 was also involved in the PI3-kinase Class IA /PKCs/STAT3 pathway. Serine phosphorylation of PDK-1 was detected in the retina from postnatal day 3. It was found that treatment of retinal explants with PDK-1 inhibitor (BX795) for four days dramatically increased the number of rod photoreceptors. On the other hand, pharmacological inhibition of PDK-1 induced a significant decline of Akt, p70S6K1, PKC-γ threonine phosphorylation and STAT3 tyrosine phosphorylation. The results indicate that PDK-1 activity is one of the critical in regulating rod photoreceptor differentiation.