Eosinophilic solid and cystic renal cell carcinomas (ESC RCC) is a rare, unique tumor type not yet included in the World Health Organization classification of renal neoplasia. Separately, RCCs found in patients with tuberous sclerosis complex (TSC) have recently been categorized into 3 morphologic groups: RCC with a tubulopapillary architecture separated by smooth muscle stroma, chromophobe-like, and eosinophilic-microcytic type. The third classification has been identified in ∼11% of TSC-associated RCC and have histology identical to ESC RCCs. The sporadic form of ESC RCC, not associated with TSC, have only been characterized on the cytogenetic level and the full molecular underpinnings have yet to be examined. Using next-generation sequencing we present 2 cases of sporadic ESC RCC in patients without clinical features of tuberous sclerosis, which demonstrate pathogenic somatic TSC2 gene mutations. These mutations are without other alterations in any other genes associated with RCC, suggesting that sporadic ESC RCC may be characterized by somatic tuberous sclerosis gene mutations (TSC2).

Eosinophilic renal neoplasms have a wide spectrum of histologic presentations, and several studies have demonstrated a subtype of renal cell carcinomas (RCCs) associated with the tuberous sclerosis complex (TSC)/mammalian target of rapamycin pathway. A review of our institutional archives led to the identification of 18 cases of renal eosinophilic tumors with unusual morphology. Immunohistochemical analysis demonstrated that these could be separated into 3 groups: group 1 had solid architecture and morphology similar to chromophobe RCC but was negative for CK20 and vimentin, and had weak focal staining for CK7 and P504S; group 2 had solid architecture and morphology similar to either renal oncocytoma or chromophobe RCC, eosinophilic variant and had diffuse staining of CK7 and P504S, absent to weak staining of CK20, and negative staining for vimentin; and group 3 had solid, cystic and papillary architecture and was negative for CK7, except for 1 case, along with moderate to strong staining of CK20, P504S, and vimentin. The cases were then sent for next-generation sequencing to determine whether molecular pathogenic variants were present. In group 1, all 3 cases had mutations in TSC2. In group 2, pathogenic variants were identified in 3 genes: TSC1, TSC2, and MTOR. In group 3, genetic alterations and pathogenic variants were identified in TSC1 and TSC2. Our results support TSC/MTOR-associated neoplasms as a distinct group that exhibits heterogenous morphology and immunohistochemical staining.

Actin is abundant in the nucleus and it is clear that nuclear actin has important functions. However, mystery surrounds the absence of classical actin filaments in the nucleus. To address this question, we investigated how polymerizing nuclear actin into persistent nuclear actin filaments affected transcription by RNA polymerase II. Nuclear filaments impaired nuclear actin dynamics by polymerizing and sequestering nuclear actin. Polymerizing actin into stable nuclear filaments disrupted the interaction of actin with RNA polymerase II and correlated with impaired RNA polymerase II localization, dynamics, gene recruitment, and reduced global transcription and cell proliferation. Polymerizing and crosslinking nuclear actin in vitro similarly disrupted the actin-RNA-polymerase-II interaction and inhibited transcription. These data rationalize the general absence of stable actin filaments in mammalian somatic nuclei. They also suggest a dynamic pool of nuclear actin is required for the proper localization and activity of RNA polymerase II.

ESR1 and GREB1 fusions have recently been described in uterine tumor resembling ovarian sex cord tumor (UTROSCT). Thus far, recurrences have been documented in a subset of those harboring GREB1 fusions, but not in those with ESR1 rearrangements. Here we describe the clinicopathologic features of 3 recurrent UTROSCTs with striking rhabdoid morphology (an unusual feature of these tumors overall) and ESR1-NCOA2 fusions. The patients were 32, 37, and 54 years at initial diagnosis and first recurrence occurred at 7, 9, and 32 years. The primary tumors (available in two cases) were centered in the myometrium and showed infiltrative borders. They predominantly grew in sheets and cords, but also had a pseudopapillary appearance. Cells were uniformly epithelioid with eccentric nuclei, prominent nucleoli, abundant eosinophilic globular/glassy (rhabdoid) cytoplasm, and infrequent mitoses (≤4/10 high-power fields [HPFs]). Recurrences were morphologically identical to the primary tumors, but demonstrated brisk mitotic activity (≥16/10 HPFs). The third tumor (with only recurrences available) had multiple patterns, including diffuse, corded, trabecular, and a focal retiform growth. Rhabdoid cells were conspicuous, but only comprised ~50% of the tumor, and mitoses numbered up to 2/10 HPFs. All tumors were strongly and diffusely positive for WT1, CAM5.2, ER, and PR, but negative for inhibin. Diffuse calretinin and desmin expression, as well as focal melan-A positivity, was noted in one tumor, but was negative in the others. In all 3 tumors, INI-1 and BRG-1 were retained, and ESR1-NCOA2 fusions were detected by targeted RNA sequencing. This study is the first to highlight an association between UTROSCTs with extensive rhabdoid differentiation, ESR1-NCOA2 fusions, and aggressive behavior. UTROSCTs are considered neoplasms of uncertain malignant potential, but have a benign course in most cases. Thus, it is important to be aware of these specific features and recommend long-term follow-up due to their propensity for late recurrences.

SUMMARYMLL2 and MLL3 histone lysine methyltransferases are conserved components of COMPASS-like co-activator complexes. In vertebrates, the paralogous MLL2 and MLL3 contain multiple domains required for epigenetic reading and writing of the histone code involved in hormone-stimulated gene programming, including receptor-binding motifs, SET methyltransferase, HMG and PHD domains. The genes encoding MLL2 and MLL3 arose from a common ancestor. Phylogenetic analyses reveal that the ancestral gene underwent a fission event in some Brachycera dipterans, including Drosophila species, creating two independent genes corresponding to the N-and C-terminal portions. In Drosophila, the C-terminal SET domain is encoded by trithorax-related (trr), which is required for hormone-dependent gene activation. We identified the cara mitad (cmi) gene, which encodes the previously undiscovered N-terminal region consisting of PHD and HMG domains and receptor-binding motifs. The cmi gene is essential and its functions are dosage sensitive. CMI associates with TRR, as well as the EcR-USP receptor, and is required for hormone-dependent transcription. Unexpectedly, although the CMI and MLL2 PHDf3 domains could bind histone H3, neither showed preference for trimethylated lysine 4. Genetic tests reveal that cmi is required for proper global trimethylation of H3K4 and that hormone-stimulated transcription requires chromatin binding by CMI, methylation of H3K4 by TRR and demethylation of H3K27 by the demethylase UTX. The evolutionary split of MLL2 into two distinct genes in Drosophila provides important insight into distinct epigenetic functions of conserved readers and writers of the histone code.