Insulin-like growth factor binding protein-3 (IGFBP-3) localizes to and modulates proliferative epidermal keratinocytes in vivo.
BACKGROUND
The colocalization of insulin-like growth factor binding protein-3 (IGFBP-3) and IGF-I receptor (IGF-IR) in the basal/germinative layer of the epidermis suggests a key role in modulating epidermal homeostasis.


OBJECTIVE
We aimed to clarify both the specific cellular localization and the effect of excess epidermal IGFBP-3 on keratinocyte proliferation.


METHODS
(i) Total RNA was isolated from fluorescence-activated cell sorted basal human keratinocyte subtypes [keratinocyte stem cells, transit amplifying keratinocytes (TA), postmitotic differentiating keratinocytes (PMD)], and real-time polymerase chain reaction analysis was used to determine the abundance of IGFBP-3 and IGF-IR mRNAs. (ii) An IGFBP-3 transgenic mouse model was then used to assess the effect of excess epidermal IGFBP-3 on keratinocyte proliferation. Excess epidermal IGFBP-3 mRNA and protein was determined by in situ hybridization and immunohistochemistry, respectively.


RESULTS
(i) The highest levels of IGFBP-3 mRNA were detected in TA keratinocytes, in contrast to IGF-IR mRNA levels which were highest in PMD keratinocytes. (ii) Elevated human IGFBP-3 mRNA and protein was confirmed in the epidermis of skin derived from transgenic mice. Excess IGFBP-3 reduced the relative percentage of proliferative keratinocytes (Ki67 positive) irrespective of skin location (belly, back and tail). Thus, in the epidermis, IGFBP-3 mRNA is highly expressed by proliferative keratinocytes (TA) and overexpression of IGFBP-3 inhibits keratinocyte proliferation.


CONCLUSIONS
We conclude that in vivo IGFBP-3 ensures epidermal homeostasis via downregulation of keratinocyte proliferation, and thus modulates the early stages of keratinocyte differentiation.
Edmondson
S R
SR
Epithelial Stem Cell Biology Laboratory, Peter MacCallum Cancer Institute, East Melbourne, 3002 Victoria, Australia.
Thumiger
S P
SP
Kaur
P
P
Loh
B
B
Koelmeyer
R
R
Li
A
A
Silha
J V
JV
Murphy
L J
LJ
Wraight
C J
CJ
Werther
G A
GA
D000328:Adult; D000818:Animals; D049109:Cell Proliferation; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008875:Middle Aged; D016133:Polymerase Chain Reaction / Q000379:methods; D012333:RNA, Messenger / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism
D018972:Insulin-Like Growth Factor Binding Protein 3; D012333:RNA, Messenger; D017526:Receptor, IGF Type 1