New insight puts CRAF in sight as a therapeutic target.

By selectively depleting components of the RAF-MEK-ERK pathway in transgenic mice, it is now shown in 2 studies that CRAF is critical for signaling to MEK downstream of oncogenic Kras and that BRAF is not required.

Molecular and genotypic characterization of human thyroid follicular cell carcinoma-derived cell lines.

OBJECTIVE: Our aim was to characterize the molecular and genotypic profile of eight thyroid carcinoma-derived cell lines-TPC1, FB2, B-CPAP, K1, XTC-1, C643, 8505C, and Hth74-in order to use them as in vitro models of thyroid carcinogenesis. DESIGN: We evaluated the expression of five thyroid-specific genes (Tg, TSHr, TPO, PAX8, and TTF-1) to establish the cell lineage and to assess the differentiation status of each of the cell lines. We screened for mutations in the most relevant oncogenes/tumor suppressor genes affected in thyroid carcinogenesis: RAS, BRAF, CTNNB1, and TP53 along with RET/PTC rearrangements. Considering the putative relevance in general carcinogenesis, we have also studied other molecules such as EGFR, PI3K, RAF-1, and THRB. To determine the genetic identity of the cell lines, we performed genotypic analysis. MAIN OUTCOME: The panel of cell lines we have studied displayed activation of several oncogenes (BRAF, RAS, RET/PTC) and inactivation of tumor suppressor genes (TP53) known to be important for thyroid carcinogenesis. Two of the cell lines-TPC1 and FB2-shared the same genotypic profile, probably representing clones of an ancestor cell line (TPC1). CONCLUSION: Due to their different molecular alterations, these cell lines represent a valuable tool to study the molecular mechanisms underlying thyroid carcinogenesis. We suggest that genotypic analyses should be included as a routine procedure to guarantee the uniqueness of each cell line used in research.

A subset of colorectal carcinomas express c-KIT protein independently of BRAF and/or KRAS activation.

c-KIT is a tyrosine kinase receptor found to be overexpressed in several tumours, namely, GISTs, breast, lung, prostate, ovarian and colorectal carcinomas (CRC). We aimed at determining the frequency of c-KIT expression and mutations in a series of 109 CRC cases (73 primary tumours and 36 lymph node metastases) characterised for KRAS and BRAF mutations. We also aimed at analysing the cellular effects of STI571/Gleevec in CRC-derived cell lines displaying c-KIT expression and KRAS or BRAF mutations. By immunohistochemistry, we found c-KIT overexpression in 15% (11/73) of primary tumours and in 14% (5/36) of metastasis; however, cases showing overexpression did not show c-kit mutations in hotspot regions. The majority (64%) of primary tumours with c-KIT overexpression had mutations at KRAS-BRAF genes. The same was true for 60% of the metastases. We treated CRC cell lines with STI571/Gleevec and verified that it inhibits proliferation and induces apoptosis in all cell lines. In conclusion, overexpression of c-KIT is observed in a subset of primary and CRC metastases in the absence of c-kit mutations. STI571/Gleevec increases apoptosis in CRC cell lines independently of its genetic profile, suggesting that STI571/Gleevec is likely to be an alternative drug for the clinical trials of CRC.

BRAF mutations typical of papillary thyroid carcinoma are more frequently detected in undifferentiated than in insular and insular-like poorly differentiated carcinomas.

Somatic mutations of the BRAF gene (BRAFV599E and BRAFK600E) were found to be closely associated with different histotypes of papillary thyroid carcinoma (PTC). The V599E mutation is highly prevalent in PTC with a papillary or mixed papillary follicular growth pattern, and the K600E mutation is apparently restricted to the follicular variant of PTC. It is usually accepted that thyroid malignancies may follow a progression path from well-differentiated to poorly differentiated (PDC) and undifferentiated (UC) carcinomas. One would expect that at least some of the less differentiated carcinomas would harbour the genetic alterations of pre-existing well-differentiated tumours. In order to find the prevalence of BRAF mutations in PDC and UC, we screened a series of 19 PDCs and 17 UCs, as well as 3 UC-derived cell lines, for both mutation types. The group of PDCs was restricted to the so-called insular and insular-like PDCs, thus excluding PTCs with solid, insular or trabecular foci of growth and PDCs displaying typical PTC nuclei. No BRAF mutations were detected in any of the 19 cases of PDC, whereas 6 of the UCs (35%) and one UC-derived cell line presented the BRAFV599E mutation. The BRAFK600E mutation was not detected in any case. We conclude that UC may progress from BRAFV599E-mutated PTC. The absence of BRAF mutations in our series of PDC supports the assumption that pure insular and insular-like PDCs are more closely related to follicular carcinoma than to PTC.