affects the degree of physical association between proliferating cell nuclear antigen (PCNA) and p300, an association that has been proposed to link DNA repair to chromatin remodeling. Together with the finding that human ING1 proteins bind PCNA in a DNA damagedependent manner, these data suggest that ING1 proteins provide a direct linkage between DNA repair, apoptosis, and chromatin remodeling via multiple HAT⅐ING1⅐PCNA protein complexes.

The ING1 candidate tumor suppressor is downregulated in a variety of primary tumors and established cancer cell lines. Blocking its expression experimentally promotes unregulated growth in vitro and in vivo, using cell and animal models. Alternative splicing products encode proteins that localize to the nucleus, inhibit cell cycle progression and affect apoptosis in different model systems. Here we show that ING1 proteins translocate to the nucleolus 12-48 h after UV-induced DNA damage. When a small 50 amino acid portion of ING1 was fused to green fluorescent protein, the fusion protein was efficiently targeted to the nucleolus, indicating that ING1 possesses an intrinsic nucleolar targeting sequence (NTS). We mapped this activity to two distinct 4 amino acid regions, which individually direct fused heterologous proteins to the nucleolus. Overexpression of ING1 induced apoptosis of primary fibroblasts in the presence and absence of UV exposure. In contrast, NTS mutants of ING1 that were not targeted to the nucleolus did not efficiently induce apoptosis when overexpressed and instead protected cells from UV-induced apoptosis. Taken together, these results indicate that UV induces ING1 to translocate to the nucleolus and that this translocation may facilitate apoptosis.

Diverse in vivo studies have suggested that adult stem cells might have the ability to differentiate into cell types other than those of the tissues in which they reside or derive during embryonic development. This idea of stem cell "plasticity" has led investigators to hypothesize that, similar to embryonic stem cells, adult stem cells might have unlimited tissue regenerative potential in vivo, and therefore, broad and novel therapeutic applications. Since the beginning of these observations, our group has critically examined these exciting possibilities for mouse bone marrow-derived cells by taking advantage of well-characterized models of tissue regeneration, Cre/lox technology, and novel stem cell isolation protocols. Our experimental evidence does not support plasticity of hematopoietic stem cells as a frequent physiological event, but rather indicates that cell fusion could account for reported cases of hematopoietic stem cell plasticity or "transdifferentiation" in vivo. Our studies highlight the need for meticulous technical controls during the isolation, transplantation, tracking, and analysis of bone marrow-derived cells during in vivo studies on plasticity. Further studies will be necessary to better define experimental conditions and criteria to unequivocally prove or reject plasticity in vivo. In this review, we focus on results from several studies from our laboratory, and discuss their conclusions and implications.

Conditional manipulation of gene expression by using tetracycline (TET)-ON based approaches has proven invaluable to study fundamental aspects of biology; however, the functionality of these systems in human embryonic stem cells (hESC) has not been established. Given the sensitivity of these cells to both genetic manipulation and variations of culture conditions, constitutive expression of TET transactivators might not only be toxic for hESC but might also impair their ability to self-renew or differentiate into multiple tissues. Therefore, the effect of these transactivators on the biology and pluripotentiality of hESC must first be evaluated before broad use of TET-ON methodologies is applied in these cells. Improved insulated lentivectors that display stable transgene expression and minimal insertional transactivation have been described for hESC. By using insulated lentivectors that allow simultaneous expression of TET components and fluorescent reporters, here we demonstrate that hESC constitutively expressing the TET-ON transactivator rtTA2SM2 can be derived and expanded in culture while retaining inducible transgene expression and pluripotentiality, including marker expression, a normal karyotype, and the ability to generate multiple tissues of different germ layer origin in teratomas. We also show that these cells retain the ability to control the expression of a stable integrated transgene in a doxycycline-dependent manner, which demonstrates that an insulated TET-ON lentiviral system is functional in hESC. Together, our results indicate that improved TET regulators like rtTA2SM2 in combination with insulated lentiviral-based systems offer alternative strategies for conditional gene expression in hESC. STEM

B-cell maturation antigen (BCMA) is selectively expressed as a surface protein on plasma cells and is a validated target for multiple myeloma (MM). A soluble form of BCMA (sBCMA) is elevated in the sera of patients with MM. The bispecific antibodies teclistamab (BCMA×CD3) and talquetamab (G protein-coupled receptor family C group 5 member D [GPRC5D]×CD3) are in clinical development as therapies for MM. Using data from patients with relapsed/refractory MM (N=300) who participated in phase 1 studies of teclistamab (NCT03145181) or talquetamab (NCT03399799), baseline serum sBCMA levels were quantitatively analyzed relative to response to treatment, percentage of bone marrow plasma cells (BMPCs), and cytogenetic risk. By cycle 3 day 1 of treatment, sBCMA levels declined from baseline in 50 (88%) of 57 responders and 49 (98%) of 50 responders to teclistamab and talquetamab, respectively. Depth of response correlated with the magnitude of sBCMA reduction. In contrast, sBCMA increased in 33 (80%) of 41 patients and 24 (49%) of 49 patients who did not respond to teclistamab or talquetamab, respectively. Baseline sBCMA levels correlated with the percentage of BMPC; patients with extramedullary plasmacytomas who had low levels of BMPC (≤10%) tended to have high baseline sBCMA levels (≥400 ng/mL), based on limited data. Baseline sBCMA levels and changes in sBCMA levels at cycle 3 day 1 were similar in patients with high- and standard-risk cytogenetics treated with teclistamab or talquetamab. These results support the use of sBCMA as a potential surrogate marker of tumor burden and treatment response in MM.