A Family With a Carotid Body Paraganglioma and Thyroid Neoplasias With a New SDHAF2 Germline Variant.

At least 30% of all pheochromocytomas (PCCs)/paragangliomas (PGLs) arise in patients with a germline predisposition syndrome. Variants in succinate dehydrogenase subunits A, B, C, and D (SDHA, SDHB, SDHC, and SDHD) are the most common pathogenic germline alterations. Few pathogenic variants have been reported in succinate dehydrogenase assembly factor 2 (SDHAF2). Here, we describe a 30-year-old female patient who presented with a left-sided neck mass, which was later characterized as a carotid body PGL. Genetic testing revealed a likely pathogenic SDHAF2 variant (c.347G>A;p.W116X). Two sisters carried the same pathologic variant, and screening protocols were recommended. Whole-body MRI revealed thyroid nodules; this testing was followed by fine-needle aspiration, which confirmed papillary thyroid carcinoma in one sister and a follicular adenoma in the other. The two sisters then underwent hemithyroidectomy and total thyroidectomy, respectively. Because evidence for pathogenic variants in SDHAF2 causing predisposition to PCC/PGL is limited, we discuss the challenges in mutational variant interpretation and decision making regarding screening for associated tumors.

Allele-specific silencing of mutant p53 attenuates dominant-negative and gain-of-function activities.

Many p53 hotspot mutants not only lose the transcriptional activity, but also show dominant-negative (DN) and oncogenic gain-of-function (GOF) activities. Increasing evidence indicates that knockdown of mutant p53 (mutp53) in cancer cells reduces their aggressive properties, suggesting that survival and proliferation of cancer cells are, at least partially, dependent on the presence of mutp53. However, these p53 siRNAs can downregulate both wild-type p53 (wtp53) and mutp53, which limits their therapeutic applications. In order to specifically deplete mutp53, we have developed allele-specific siRNAs against p53 hotspot mutants and validated their biological effects in the absence or presence of wtp53. First, the mutp53-specific siRNAs selectively reduced protein levels of matched p53 mutants with minimal reduction in wtp53 levels. Second, downregulation of mutp53 in cancer cells expressing a mutp53 alone (p53mut) resulted in significantly decreased cell proliferation and migration. Third, transfection of mutp53-specific siRNAs in cancer cells expressing both wtp53 and mutp53 also reduced cell proliferation and migration with increased transcripts of p53 downstream target genes, which became further profound when cells were treated with an MDM2 inhibitor Nutlin-3a or a chemotherapeutic agent doxorubicin. These results indicate that depletion of mutp53 by its specific siRNA restored endogenous wtp53 activity in cells expressing both wtp53 and mutp53. This is the first study demonstrating biological effects and therapeutic potential of allele-specific silencing of mutp53 by mutp53-specific siRNAs in cancer cells expressing both wtp53 and mutp53, thus providing a novel strategy towards targeted cancer therapies.