Indiana University-Purdue University Indianapolis (IUPUI) / Human skin, consisting of the outer epidermis and inner dermis, serves as
a barrier that protects the body from an onslaught of environmental stresses.
Keratinocytes in the stratified epidermis undergo sequential differentiation that
consists of multiple layers of cells differing in structure and function. Therefore,
keratinocytes must not only combat environmental stress, but need to undergo
massive changes in gene expression and morphology to form a proper barrier.
One mode by which cells cope with stress and differentiation is through
phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α-P), which
causes global inhibition of protein synthesis coincident with preferential
translation of select gene transcripts. Translational repression allows stressed
cells to conserve energy and prioritize pro-survival processes to alleviate stress
damage. Since eIF2α kinases are each activated by distinct types of stress, this
pathway is referred to as the Integrated Stress Response (ISR). We sought to
identify the roles of the ISR in the keratinocyte response to the stresses
associated with differentiation and ultraviolet B (UVB) irradiation.
In this thesis, we show that both general and gene-specific translational
control in the ISR are activated following differentiation or UVB irradiation of
human keratinocytes. ISR deficiency through genetic modifications or pharmacological interventions caused severe divergence from the appropriate
keratinocyte response to differentiation or UVB. Differentiation genes were
selectively translated by eIF2α-P, and inhibition of the ISR diminished their
induction during differentiation. Furthermore, loss of the eIF2α kinase GCN2
(EIF2AK4) adversely affected the ability of keratinocytes to stratify in three
dimensional cultures. Our analysis also revealed a non-canonical ISR response
following UVB irradiation, in which downstream factors ATF4 (CREB2) and
CHOP (DDIT3/GADD153) were poorly expressed due to repressed transcription,
despite preferential translation in response to eIF2α-P. The ISR was
cytoprotective during UVB and we found that eIF2α-P was required for a UVB
induced G1 arrest, cell fate determination, and DNA repair via a mechanism
involving translational control of human CDKN1A (p21 protein) transcript variant
4 mRNA. Collectively, this thesis describes novel roles for the ISR in keratinocyte
differentiation and response to UVB, emphasizing the utility of targeting
translational control in skin disease therapy.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/13386 |
| Date | 03 May 2017 |
| Creators | Collier, Ann E. |
| Contributors | Spandau, Dan F., Wek, Ronald C., Travers, Jeffrey B., Turchi, John J., Turner, Matthew J. |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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