A Novel Gene Expressed in Human Keratinocytes with Long-Term In Vitro Growth Potential is Required for Cell Growth

Abstract

The herpes simplex virus large subunit of ribonucleotide reductase differs from its counterparts in eukaryotic and prokaryotic cells and in other viruses in that it contains a unique domain that codes for a distinct serine-threonine protein kinase that activates the Ras/MEK/MAPK mitogenic pathway and is required for virus growth. Previous studies suggested that ribonucleotide reductase protein kinase was co-opted from a cellular gene. Cellular genes similar to ribonucleotide reductase protein kinase were not cloned, however, and their function is unknown. Here we report that a novel gene (H11) that codes for a protein similar to herpes simplex virus 2 ribonucleotide reductase protein kinase, is expressed in skin tissues, cultured keratinocytes, and the keratinocyte cell line A431. The protein is phosphorylated and it associates with the plasma membrane. H11 is expressed in keratinocytes with long-term in vitro growth potential and is coexpressed with high levels of adhesion molecules involved in signal transduction, such as beta1 integrin. Antisense oligonucleotides that inhibit H11 expression inhibit DNA synthesis and keratinocyte proliferation, suggesting that H11 expression is required for cell growth.

Forced Expression of the H11 Heat Shock Protein Can Be Regulated by DNA Methylation and Trigger Apoptosis in Human Cells

“…The percentage of apoptotic cells increased with time after H11 induction and was maximal at 7-9 days post-treatment (4 -6 days after induction of H11 expression). However, heat shockinduced H11 overexpression did not trigger apoptosis in HEK293 cells, and H11 is abundantly expressed in proliferating (basal) keratinocytes (30), suggesting that its apoptotic activity is cell type-specific.…”

“…Our studies were stimulated by previous observations that H11, the eukaryotic homologue of a viral protein with cell regulatory potential, differs from canonical Hsp in that it is associated with the cell surface, has auto-and transphosphorylating PK activity, is silenced by cell differentiation (18,21,30), and does not translocate to the nucleus upon heat shock. 2 Multiple tissue arrays confirmed previous reports that constitutive H11 expression is tissue-restricted, with a hierarchy and distribution pattern similar to that of other members of the small Hsp subfamily (38).…”

The Herpes Simplex Virus Type 2 R1 Protein Kinase (ICP10 PK) Functions as a Dominant Regulator of Apoptosis in Hippocampal Neurons Involving Activation of the ERK Survival Pathway and Upregulation of the Antiapoptotic Protein Bag-1

“…Previous studies have shown that (i) expression of ICP10 PK is required for stress-induced HSV-2 reactivation from ganglionic latency (3) and (ii) ICP10 PK is homologous to a newly identified heat shock protein (4,77). Together with these findings and recent conclusions that the heat shock protein gene family is a distinct class of apoptosis regulatory proteins (28), our data indicate that expression of heat shock protein homologues is a novel mechanism for virus-induced antiapoptotic activity.…”

Interaction of Human HSP22 (HSPB8) with Other Small Heat Shock Proteins

“…While in this and other reports HSP22 was characterized as an sHSP (2,3), in some reports the newly described protein was classified as a protein kinase with similarity to the Herpes simplex protein kinase ICP10 (4 -6). HSP22 occurs preferentially in striated and smooth muscles, but also in brain (1), estrogen receptorpositive breast cancer cells (2), melanoma cells (4), and keratinocytes (5). In addition to HSP22, also abundant in muscles are other sHSPs including HSP27, myotonic dystrophy kinasebinding protein (MKBP, HSPB2), HSPB3, ␣B-crystallin (␣B-Cry, HSPB5), HSP20 (HSPB6), and cvHSP (HSPB7) (7,8).…”