Regulation of skin tumorigenesis by integrin α3β1

Integrins are αβ heterodimeric adhesion receptors that play an important role
in maintaining epithelial integrity. In the skin, the major integrins α2β1,
α3β1 and α6β4 connect the cytoskeleton of basal keratinocytes to the underlying
basement membrane. Besides their key function in skin physiology, these
integrins also have been implicated in the development and progression of SCCs.
Mouse models in which different integrins are either overexpressed in the
suprabasal epidermis or mutated in the whole animal showed altered
susceptibilities to chemically induced skin tumorigenesis. Increased expression
of α2β1, α3β1 and α6β4 has been observed in hyperproliferating human cancers of
the head and neck. Integrins thus seem to play a role in the initiation and
promotion of tumors.
The integrin α3β1 is one of two receptors (the other being α6β4) expressed by
basal keratinocytes that bind to laminin-332 and -511 in the epidermal basement
membrane. It forms a stable complex with the tetraspanin CD151, which
strengthens the adhesion mediated by α3β1. Recently, we showed using
epidermis-specific knockout mice for the genes encoding the α3 subunit (Itga3)
or CD151 (Cd151) that both genes are required for the efficient formation of
skin tumors following exposure to carcinogen (1,2). In the absence of α3β1,
epidermal turnover is increased leading to depletion of slow-cycling
keratinocytes, which are thought to be the cells-of-origin of epidermal cancer.
Loss of α3β1 in benign tumors reduces proliferation, but increases tumor
progression in advanced SCCs. Similar effects are observed in
epidermis-specific Cd151-knockout mice. Epidermal turnover is associated with
loss of slow-cycling keratinocytes. As a result, fewer tumors are formed after
exposure to carcinogen. In contrast to the consequences of the loss of α3β1,
these effects are dependent on the presence of TPA that increases proliferation
and migration, but decreases adhesion.

The primary objective is to evaluate possible clinical effects correlated with
α3β1 and CD151 expression in human epidermal malignancies, and relate these
findings to the effects of α3β1 and CD151 deficiencies in skin cancer in the
mouse. Specifically, we will determine whether in benign hyperplasic lesions of
the skin (actinic keratosis, keratoacanthoma) the expression of α3β1 and CD151
is increased, but decreased if they are malignant transformed into squamous
cell carcinomas (SCCs) in situ (Bowen disease) and subsequent progression to
invasive SCCs and spindle/anaplastic SCCs. Unfortunately, none of the
commercially available antibodies against human α3 and CD151, reliably react
with formalin-fixed paraffin-embedded (FFPE) tissues. Therefore we wish to
examine the expression of these antigens as well as those of associated
proteins (e.g. FAK, ILK, etc) on freshly frozen normal, pre-malignant and tumor
material. It is anticipated that for these (pilot) experiments we will need
eight skin biopsies for each type of lesion from different patients.
Establishing a correlation between the expression of α3β1 and the histological
grade in human skin cancer may provide important prognostic and therapeutic
information.

This is an observational study, investigating the expression pattern of
integrins and associated proteins on frozen sections of normal skin, keratosis
actinica, etc. It concerns a pilot experiment exploring the possibility whether
there is a correlation between the level of expression of these proteins and
the grade of tumor. The experiment involves groups of 8 patients each with a
distinct type of tumor. As a control we will compare the level of expression of
the various proteins in the different types of tumors with that in normal skin
obtained from the same patient. If the results of these preliminary experiments
are promising we will expand the study by including more patients to render the
data statistically significant.

The burden and risks associated with participation in this study are negligible
.