RAC1 Alterations Induce Acquired Dabrafenib Resistance in Association with Anaplastic Transformation in a Papillary Thyroid Cancer Patient

BRAF-activating mutations are the most frequent driver mutations in papillary thyroid cancer (PTC). Targeted inhibitors such as dabrafenib have been used in advanced BRAF-mutated PTC; however, acquired resistance to the drug is common and little is known about other effectors that may play integral roles in this resistance. In addition, the induction of PTC dedifferentiation into highly aggressive KRAS-driven anaplastic thyroid cancer (ATC) has been reported. We detected a novel RAC1 (P34R) mutation acquired during dabrafenib treatment in a progressive metastatic lesion with ATC phenotype. To identify a potential functional link between this novel mutation and tumor dedifferentiation, we developed a cell line derived from the metastatic lesion and compared its behavior to isogenic cell lines and primary tumor samples. Our data demonstrated that RAC1 mutations induce changes in cell morphology, reorganization of F-actin almost exclusively at the cell cortex, and changes in cell adhesion properties. We also established that RAC1 amplification, with or without mutation, is sufficient to drive cell proliferation and resistance to BRAF inhibition. Further, we identified polyploidy of chromosome 7, which harbors RAC1, in both the metastatic lesion and its derived cell line. Copy number amplification and overexpression of other genes located on this chromosome, such as TWIST1, EGFR, and MET were also detected, which might also lead to dabrafenib resistance. Our study suggests that polyploidy leading to increased expression of specific genes, particularly those located on chromosome 7, should be considered when analyzing aggressive thyroid tumor samples and in further treatments.

Neoadjuvant BRAF- and Immune-Directed Therapy for Anaplastic Thyroid Carcinoma

Anaplastic thyroid cancer (ATC) is a devastating disease with a dismal prognosis. Patients who have disease confined to the thyroid and who are able to undergo complete surgery and chemoradiation stand the best chance for survival. Unfortunately, nearly 50% of patients have distant metastases at diagnosis, and most present with locally advanced, unresectable tumors. Nevertheless, BRAF-mutated ATC patients represent a subset of cases who can benefit from a combination therapy with BRAF and MEK inhibitors. Here, a patient is presented with end-stage, locally advanced, unresectable ATC who was treated with this combination. Immunotherapy with pembrolizumab was added at the first sign of progression after which he achieved a partial response to therapy, enabling a complete surgical resection followed by postoperative chemoradiation to be undertaken. This novel neoadjuvant approach to BRAF-mutated ATC should be studied in further in clinical trials.

The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Immunomagnetic isolation and long-term culture of mouse type A spermatogonia

In the mammalian testis, type A spermatogonia proliferate and differentiate into sperm under the tight control of both endocrine and paracrine factors. In order to study the complex process of spermatogenesis at the molecular level, an in vitro system must be devised in which type A spermatogonia can be cultured for a prolonged period of time. Therefore, cocultures including type A spermatogonia and Sertoli cells, which act as nurse cells to the developing germ cells, are desirable. We have developed a method for the specific isolation of type A spermatogonia using magnetic beads and antibodies that recognize the c-kit receptor or the homophilic adhesion molecule, Ep-CAM. Purified spermatogonia could survive for a period of 25 days when cocultivated on Sertoli cell monolayers. Moreover, we recently established Sertoli cell lines that produce growth factors that are essential for the maintenance of spermatogonia in a proliferative state. Some of these Sertoli cell lines are able to reorganize into tubular structures when cultivated on a layer of Matrigel as extracellular matrix. We show here that type A spermatogonia associate specifically with the Sertoli cell tubules, and are able to replicate their DNA in this environment. Thus, these in vitro culture systems could be used for the long-term culture of primary, nonimmortalized type A spermatogonia.

Establishment of a shear stress protocol to study the mechanosensitivity of human primary osteogenic cells in vitro

We report here the establishment of a protocol to study the influence of mechanical stress on the behavior of primary human osteogenic cells. We first developed a method for the specific isolation of human bone marrow osteoprogenitors and studied their potential of differentiation into osteoblasts in vitro. Then, using NIH-3T3 cells as a model for cells of mesenchymal origin, we employed a parallel plate flow chamber apparatus to apply shear stress to cells in culture. This technique will be useful to determine the influence of shear stress on the rate of proliferation and differentiation of human osteoprogenitors and osteoblasts. Ultimately, this line of research will extend our knowledge on osteogenesis and bone remodeling.

Transcriptional pathways induced by fluid shear stress in mouse preosteoblast cells

Recent findings support the idea that fluid movement in the bone is a key factor in bone formation and related cellular responses. However, the precise molecular mechanisms are not known. Our data demonstrates that fluid shear stress is a key factor in the activation of specific transcriptional pathways in murine preosteoblast (MC3T3E1) cells. MC3T3E1 cells have increased expression of the egr-1 and p57kip2 genes after being subjected to 0.3 dynes/cm2 of fluid shear stress. The MC3T3E1 cells are already known to express egr-1, a multipotent transcription factor, after high levels of fluid shear stress, but this is the first demonstration of egr-1 expression after low levels of fluid shear stress. Moreover, this is the first study showing expression of p57kip2 by the MC3T3E1 cells after fluid shear stress. The expression of p57kip2, a cyclin dependent kinase inhibitor, is a strong indicator that the cells are exiting the cell cycle and are beginning to differentiate. Our data shows decreased 3H-thymidine incorporation up to 18 hours post stress, which agrees with the upregulation of p57kip2 as a result of fluid shear stress.

An in vitro tubule assay identifies HGF as a morphogen for the formation of seminiferous tubules in the postnatal mouse testis

We have been working with a recently immortalized Sertoli cell line, SF7, that appears to produce sleeves, or hollow tubules, when cultivated on a layer of growth factor-reduced Matrigel (GFR-Matrigel) in medium supplemented with serum. We tried to determine which components of GFR-Matrigel and serum provide the environment needed for tubule formation. While laminin and collagen IV were essential for the formation of flat cords, none of the basement membrane constituents, when taken alone or in combination, would support the formation of tubules in minimal culture medium. Moreover, none of the growth factors present in GFR-Matrigel could induce tubulogenesis. Recently, much attention has been focused upon the role of hepatocyte growth factor (HGF) and its receptor c-met in the induction of tubulogenesis by epithelial cells. Therefore, we investigated the expression of HGF/c-met in the mouse testis at different postnatal stages and in the adult and evaluated the contribution of HGF/c-met in the production of Sertoli cell tubules by SF7 and primary Sertoli cells in vitro. Our results confirm that laminin and collagen IV are essential for the formation of testicular cords and reveal that HGF/c-met are necessary for the further remodeling of these cords into tubules.

Immunomagnetic isolation of osteoprogenitors from human bone marrow stroma

We report here the efficient and specific isolation of human bone marrow osteoprogenitors using magnetic beads coated with a mouse mAb (STRO-1) that recognizes a stromal cell surface protein. According to their pattern of differentiation, osteoprogenitors accounted for 100% of the STRO-1-positive cell population. Upon long term culture, osteoprogenitors differentiated down the osteoblastic lineage as evidenced by their in vitro morphology, their increased expression of alkaline phosphatase, their production of osteocalcin, and the deposition of a mineralized matrix. Upon differentiation, the cells first expressed alkaline phosphatase on their surface before they began proliferating as phenotypically recognizable osteoblasts. This observation conflicts with previous studies that have characterized human osteoprogenitors as highly proliferative cells that form colonies before differentiating into osteoblasts. The ability to isolate and cultivate pure populations of primary human osteoprogenitors will substantially advance investigations on osteogenesis and bone remodeling.

Refinement of the differentiated phenotype of the spermatogenic cell line GC-2spd(ts)

A transformed spermatogenic cell line GC-2spd(ts), recently reported to express a protein marker of spermiogenesis, was tested for the presence of several mRNAs encoded by genes transcribed specifically in the testis and at precise stages of spermatogenesis. Northern blotting and reverse-transcriptase polymerase chain reaction techniques showed that mRNAs for the stage-specific marker proteins LDH-C4 (preleptotene), acrosin (premeiotic), protamine-2 (postmeiotic), and SP-10 (postmeiotic round spermatid stage) were not detected in GC-2spd(ts) cells. Flow cytometric analysis of GC-2spd(ts) failed to detect a peak indicative of the presence of haploid chromosomes. Furthermore, the HS-63 monoclonal antibody, employed in an earlier report to demonstrate putative proacrosomal granules, failed to recognize the SP-10 protein in extracts of human or mouse sperm or in GC-2spd(ts) cells and instead recognized proteins of different masses. In view of interest in this line as a model for analyzing molecular events of spermatogenesis, this refinement of the GC-2spd(ts) phenotype may aid others considering these cells for studies of terminal stages of sperm differentiation.

Can insights into urodele limb regeneration be achieved with cell cultures and retroviruses?

Recent advances in the field of amphibian limb regeneration have provided insights into its cellular and molecular events. This review summarizes the development of cell lines from limb tissues and their application to the study of transdifferentiation and limb regeneration. In addition, the availability of suitable retroviral vectors for salamanders is discussed for it has opened new avenues for experimentation at the molecular level.

A haploid and a diploid cell coexist in an in vitro immortalized spermatogenic cell line

We have recently established a conditionally immortalized germ cell line [GC-2spd(ts)] that, at the permissive temperatures of 37 degrees C and 32 degrees C, is able to undergo meiosis in vitro and form round spermatids [Hofmann et al., (1994): Proc Natl Acad Sci USA 91:5533-5537]. In this report, we provide data that indicate that the GC-2spd(ts) cell line consists of two cell populations undergoing a haploid (n/2n) cell cycle and a diploid (2n/4n) cell cycle, respectively. The cells containing 2n DNA, when sorted by fluorescence-activated cell sorting, are able to reconstitute the full population of n/2n/4n DNA cells, indicating that they are able to commit to the reductive meiotic division and form haploid spermatids or to continue self-replication through a diploid cell cycle. This GC-2spd(ts) cell line provides a valuable tool to study the molecular mechanisms involved in the cellular decision between self-renewal by mitosis and commitment to meiosis.

Immortalized germ cells undergo meiosis in vitro

Establishing mammalian germ-cell lines capable of differentiation in vitro would greatly facilitate the study of gametogenesis and the meiotic process that is so fundamental for reproduction and the maintenance of genetic diversity of the species. We have established two germ-cell lines [GC-2spd(ts) and GC-3spc(ts)] by cotransfecting primary mouse testicular germ cells with the simian virus 40 large tumor antigen gene and the gene coding for a temperature-sensitive mutant of p53. Both cell lines express the germ cell-specific lactate dehydrogenase C4 isozyme and cytochrome ct isoform. At the permissive temperature of 37 degrees C, the GC-2spd(ts) line generates cells with a haploid DNA content and morphologic and biochemical features of round spermatids, including the appearance of an acrosomic granule. The identification of a flagellar axoneme when these cells are cultured at 32 degrees C further indicates that these cells correspond to the early spermatid stages of spermiogenesis.

Genomic structure and promoter activity of the human testis lactate dehydrogenase gene

The structure of the gene encoding the human testis-specific isozyme of lactate dehydrogenase (LDH) has been characterized and a regulatory region identified by promoter activity. The single-copy ldh-c gene has two alternative 5' noncoding exons and seven coding exons comprising an approximately 40-kb locus. The gene does not contain the canonical TATA or CAAT promoter sequences, and ribonuclease protection experiments suggest multiple transcription start sites. In the present study an immortalized murine germ cell line was used to detect promoter activity driven by 5' sequence of human ldh-c with lacZ as the reporter gene. Reporter gene activity was nondetectable when promoter constructs were transfected into nongerminal cells.

Developmental expression of alkaline phosphatase genes; reexpression in germ cell tumours and in vitro immortalized germ cells

Human germ cell alkaline phosphatase (GCAP) is developmentally expressed in primordial germ cells and in trace amounts in the testis and thymus. The equivalent mouse isozyme, embryonic alkaline phosphatase (EAP), is similarly expressed in the testis and thymus but also from the 2-cell to blastocyst stage of preimplantation development. EAP has been found to be transiently expressed in M-phase spermatogenic cells in the mouse testis. These alkaline phosphatase isozymes serve as markers of germ cell differentiation and in the management of germ cell tumors. GCAP is expressed in carcinoma-in-situ and seminoma where serum GCAP levels are often elevated and may provide clinically useful information. However, GCAP is a polymorphic enzyme, and monoclonal antibodies to be used in the clinical evaluation of tumor tissues or fluids should be carefully evaluated for their ability to detect all allelic variants of GCAP.

Embryonic alkaline phosphatase is expressed at M-phase in the spermatogenic lineage of the mouse

We have recently cloned and characterized a novel embryonic alkaline phosphatase (EAP) expressed at the two-cell to blastocyst stage of preimplantation development in the mouse. The isozyme is re-expressed in trace amounts in the thymus, intestine and testis during adult life. In the present report, we find that EAP transcripts can be detected, by RT-PCR analysis, in very low amounts in the testes of newborn mice, but at 24 days of age EAP mRNA levels reach the highest concentrations, remaining high at 40 and even 117 days of age. We produced a synthetic peptide and a corresponding rabbit anti-peptide antiserum (Rb-1434), which was characterized by enzyme antigen immunoassays and reactivity with chinese hamster ovary cell transfectants, as reacting specifically with EAP. The Rb-1434 antibody enabled us to examine immunohistochemically what cell types in the testis are responsible for the expression of EAP during different developmental stages. No positive cells were recognized in the testis of newborns (day 0) and 8-day-old mice. Positive cells were first observed at day 15 and, at 24 days of age, many positive M-phase cells, morphologically corresponding to spermatocytes in mid to late prophase of meiotic division I, were strongly positive for EAP expression. Positive M-phase cells were also observed at 40 days and 151 days of age. Transgenic mice expressing the human GCAP isozyme in a tissue-specific manner in the testis, showed equivalent stages of M-phase figures when stained immunohistochemically with a specific rabbit polyclonal antiserum.(ABSTRACT TRUNCATED AT 250 WORDS)

Immortalization of germ cells and somatic testicular cells using the SV40 large T antigen

We report the immortalization, using the SV40 large T antigen, of all the cell types contributing to a developing seminiferous tubule in the mouse testis. Sixteen peritubular, 22 Leydig, 8 Sertoli, and 1 germ cell line have been established and cultured successfully for 90 generations in a period of 2.5 years. Immortalized peritubular cells were identified by their spindle-like appearance, their high expression of alkaline phosphatase, and their expression of the intermediary filament desmin. They also produce high amounts of collagen. Immortalized Leydig cells are easily identifiable by the accumulation of lipid droplets in their cytoplasm and the production of the enzyme 3-beta-hydroxysteroid dehydrogenase. Some Leydig cell lines also express LH receptors. The immortalized Sertoli cells are able to adopt their typical in vivo columnar appearance when cultured at high density. They exhibit a typical indented nucleus and cytoplasmic phagosomes. Some Sertoli cell lines also express FSH receptors. A germ cell line (GC-1spg) was established that corresponds to a stage between spermatogonia type B and primary spermatocyte, based on its characteristics in phase contrast and electron microscopy. This cell line expresses the testicular cytochrome ct and lactate dehydrogenase-C4 isozyme. These four immortalized cell types, when plated together, are able to reaggregate and form structures resembling two-dimensional spermatogenic tubules in vitro. When only the immortalized somatic cells are cocultured, the peritubular and Sertoli cells form cord-like structures in the presence of Leydig cells. Fresh pachytene spermatocytes cocultured with the immortalized somatic cells integrate within the cords and are able to survive for at least 7 days. The ability to perform coculture experiments with immortalized testicular cell lines represents an important advancement in our ability to study the nature of cell-cell and cell-matrix interactions during spermatogenesis and testis morphogenesis.

Supernumerary chromosome 1 in interphase nuclei of atypical germ cells in paraffin-embedded human seminiferous tubules

The so-called atypical germ cells or cells of carcinoma in situ morphologically resemble neoplastic cells in seminoma. Since seminomas show numerical aberrations of chromosome 1 we have used a DNA probe specific for chromosome region 1q12 to determine whether such aberrations can be detected in atypical germ cell nuclei in paraffin-embedded seminiferous tubules as well. One-third of intratubular nuclei, containing atypical germ cells, consistently showed three hybridization signals in contrast to two signals regularly observed in normal intestine and in spermatogonia. We thus show that cytogenetic studies of precancerous cells can be performed directly on the tissue where these cells originate.

Alkaline phosphatase isozymes in human testicular germ cell tumors, their precancerous stage, and three related cell lines

The four known isozymes of the human alkaline phosphatase (ALP) were detected by isoelectric focusing in extracts of various types of germ cell tumors, three related cell lines, and their precancerous elements (atypical germ cells). In seminoma, placental alkaline phosphatase (PLAP) and germ cell alkaline phosphatase (PLAP-like) could be separated by isoelectric focusing following isolation by immunoaffinity. The occurrence of both isozymes in seminoma could explain partial heat sensitivity and variation in electrophoretic patterns of the seminoma isozyme frequently observed upon starch gels, in comparison to the normal placental phenotype. The four ALP isozymes are produced not only in germ cell tumors, but already in precancerous tissues. Quantitative analysis showed that the amount of the four isozymes varies in parallel in the tumors tested. Maximal expression was found in seminoma. The relation between ALP gene overexpression and gene amplification by polyploidy of chromosomes 1 and 2 in these lesions is discussed. On the other hand, the ectopic expression of intestinal alkaline phosphatase and PLAP associated with overexpression of PLAP-like in tumor cells as well as in their precancerous stage indicates gene activation by some unknown mechanisms, probably a regulatory process affecting the three tissue-specific ALP genes simultaneously.

Interphase cytogenetics in paraffin embedded sections from human testicular germ cell tumor xenografts and in corresponding cultured cells

A protocol was developed that allows determination of chromosome aberrations in interphase nuclei from paraffin embedded human tissues. As a model system tissue sections from xenografts derived from three testicular germ cell tumors (two teratocarcinoma and one embryonal carcinoma), as well as sections from normal intestine and testicular tissues, were hybridized with a biotin-labeled DNA probe specific for 1q12. For comparison, isolated nuclei in suspension and metaphase spreads from in vitro cell lines derived from the respective xenografts were assayed. Our results show that interphase tumor cells with aberrant numbers of chromosome 1 can be reliably detected both in vitro and in vivo. Subclones with two and three labeled chromosomes, respectively, could be defined and quantitatively evaluated. Present and future possibilities to pinpoint specific chromosome aberrations directly in cells present in body fluids or in tumor tissues are discussed.