Expression Profile of Receptor-Type Protein Tyrosine Kinase Genes in the Human Thyroid

Abstract

Protein tyrosine kinases (PTKs) play a role in regulating the growth and differentiated functions of thyroid cells and are probably involved in tumorigenesis of papillary-type thyroid carcinoma. To better understand the roles of PTKs in the physiology and pathophysiology of the thyroid, we analyzed the expression profile of receptor-type PTKs in normal human thyroid tissues. Highly conserved regions in the catalytic domains of receptor-type PTKs were amplified by RT-PCR using degenerate oligonucleotide primers. Nucleotide sequencing of about 100 clones identified 21 PTKs, including 16 receptor type and 5 nonreceptor type; no novel PTK was identified. Insulin-like growth factor I receptor, platelet-derived growth factor receptor (PDGFR), TrkE, Axl, epidermal growth factor receptor, etc., appear to be the most abundant receptor-type PTKs in the thyroid; many of which (PDGFR, TrkE, Axl, etc.) have never previously been demonstrated to be expressed in the thyroid. The expression of messenger RNAs (mRNAs) for PDGFR, axl, and trkE in normal thyroid cells was confirmed by Northern blot analysis, and interestingly, the expression levels of PDGFR and trkE mRNAs were decreased in all three thyroid carcinoma cell lines examined (FRO, WRO, and NPA), whereas axl mRNA and protein were overexpressed in 2 of 3 thyroid carcinoma cell lines (FRO and WRO) compared with that in normal tissue. The axl gene was, however, neither amplified nor rearranged. The biological activity of the ligand for Axl, the product of growth arrest-specific gene 6 (Gas6), was then evaluated, demonstrating modest mitogenic activity in thyroid carcinoma cells overexpressing Axl. Furthermore, gas6 mRNA was expressed in FRO cells.Thus, we here identify a variety of PTKs expressed in the thyroid gland, many of which may participate in the regulation of thyroid cell function. Variable expression levels of some PTKs in normal and cancerous cells suggest that there may be an imbalance and disarray of phosphorylation events in thyroid carcinoma cells. Furthermore, Gas6 is identified as a novel growth factor for thyroid carcinoma cells overexpressing Axl receptor tyrosine kinase. (Endocrinology 139: 852-858, 1998) P ROTEIN tyrosine kinases (PTKs) are believed to play a pivotal role in regulating the growth and differentiated functions of eukaryotic cells as components of signal transduction pathways (1). The PTK family is classified into receptor type and nonreceptor type (cytoplasmic type), and includes cellular receptors for certain growth factors and protooncogenes (2).In thyroid cells, activation of PTK cascades, for example, by epidermal growth factor (EGF) and fibroblast growth factor (FGF) are closely linked to cell proliferation and dedifferentiation (3). On the other hand, TSH, a pituitary glycoprotein hormone that is indispensable for stimulating both thyroid cell proliferation and differentiation and largely functions through the cAMP-protein kinase A (serine/threonine kinase)-dependent signal transduction cascade and, to a lesser extent, the C...

RT-PCR-based tyrosine kinase display profiling of canine melanoma: IGF-1 receptor as a potential therapeutic target

“…Among the receptor TKs were Axl, To begin to elucidate the spectrum of TKs expressed in CMM, an RT-PCR display technique was used using cDNA generated from the 17CM98 CMM cell line. The PCR reaction resulted in a single 210-bp band, the expected size based on human studies [9], and omission of reverse transcriptase resulted in the absence of any detectable product (not shown). This band, containing a variety of kinase sequences, was cut out, the product ligated into a cloning vector, E. coli was transformed, and bacterial colonies carrying an insert-containing plasmid picked using standard blue-white screening.…”

“…Before using this technique in another species, it was important to determine the degree of conservation of these kinase domains in dogs. A BLASTp search of the translated canine genome using the HRDLAARN and DVWS(F/Y)G(I/V) peptide motifs described by Tanaka et al [9] yielded 32 canine TKs sharing these motifs. Among the receptor TKs were Axl, To begin to elucidate the spectrum of TKs expressed in CMM, an RT-PCR display technique was used using cDNA generated from the 17CM98 CMM cell line.…”

“…Degenerate oligonucleotide primers coding for the amino acid sequences HRDLAARN and DVWS(F/Y)G(I/V), in the RTK catalytic domains, were used as described earlier [9]. The specific PCR primers were 5…”

“…This technique exploits the fact that there are highly conserved amino acid regions flanking the kinase domains of many TKs, to which a single set of degenerate PCR primers can be designed [9]. Given the large percentage of sequenced clones coding for Supplemental digital content is available for this article.…”

Structural Elucidation of the DFG-Asp in and DFG-Asp out States of TAM Kinases and Insight into the Selectivity of Their Inhibitors

“…TAM kinases were initially found in cancer cells [4,5,6,7], which lead to the discovery that overexpression or ectopia of these RTKs contribute to carcinogenesis [8,9,10]. Indeed, many cancers, including cancers of the uterine endometrium [8], stomach [11,12], colon [13], prostate [14,15,16,17], thyroid [18,19,20], lung [21,22], breast [23,24,25,26], ovaries [27,28], liver [29] and kidneys [9], as well as glioblastomas [30], melanomas [31,32,33], osteosarcomas [34], leukemias [4,35,36] and multiple myelomas [37] exhibit altered expression of one or more TAM members [3]. Interestingly, among the three TAM members, Axl has been found to be the most involved in human cancers [3].…”