Tissues can be soft like fat, which bears little stress, or stiff like bone, which sustains high stress, but whether there is a systematic relationship between tissue mechanics and differentiation is unknown. Here, proteomics analyses revealed that levels of the nucleoskeletal protein lamin-A scaled with tissue elasticity, E, as did levels of collagens in the extracellular matrix that determine E. Stem cell differentiation into fat on soft matrix was enhanced by low lamin-A levels, whereas differentiation into bone on stiff matrix was enhanced by high lamin-A levels. Matrix stiffness directly influenced lamin-A protein levels, and, although lamin-A transcription was regulated by the vitamin A/retinoic acid (RA) pathway with broad roles in development, nuclear entry of RA receptors was modulated by lamin-A protein. Tissue stiffness and stress thus increase lamin-A levels, which stabilize the nucleus while also contributing to lineage determination.

Interaction of spherical particles with cells and within animals has been studied extensively, but the effects of shape have received little attention. Here we use highly stable, polymer micelle assemblies known as filomicelles to compare the transport and trafficking of flexible filaments with spheres of similar chemistry. In rodents, filomicelles persisted in the circulation up to one week after intravenous injection. This is about ten times longer than their spherical counterparts and is more persistent than any known synthetic nanoparticle. Under fluid flow conditions, spheres and short filomicelles are taken up by cells more readily than longer filaments because the latter are extended by the flow. Preliminary results further demonstrate that filomicelles can effectively deliver the anticancer drug paclitaxel and shrink human-derived tumours in mice. Although these findings show that long-circulating vehicles need not be nanospheres, they also lend insight into possible shape effects of natural filamentous viruses.

Migration through micron-size constrictions has been seen to rupture the nucleus, release nuclear-localized GFP, and cause localized accumulations of ectopic 53BP1 – a DNA repair protein. Here, constricted migration of two human cancer cell types and primary mesenchymal stem cells (MSC) increases DNA breaks throughout the nucleoplasm as assessed by endogenous damage markers and by electrophoretic ‘comet’ measurements. Migration also causes multiple DNA repair proteins to segregate away from DNA, with cytoplasmic mis-localization sustained for many hours as is relevant to delayed repair. Partial knockdown of repair factors that also regulate chromosome copy numbers is seen to increase DNA breaks in U2OS osteosarcoma cells without affecting migration and with nucleoplasmic patterns of damage similar to constricted migration. Such depletion also causes aberrant levels of DNA. Migration-induced nuclear damage is nonetheless reversible for wild-type and sub-cloned U2OS cells, except for lasting genomic differences between stable clones as revealed by DNA arrays and sequencing. Gains and losses of hundreds of megabases in many chromosomes are typical of the changes and heterogeneity in bone cancer. Phenotypic differences that arise from constricted migration of U2OS clones are further illustrated by a clone with a highly elongated and stable MSC-like shape that depends on microtubule assembly downstream of the transcription factor GATA4. Such changes are consistent with reversion to a more stem-like state upstream of cancerous osteoblastic cells. Migration-induced genomic instability can thus associate with heritable changes.

Highlights d Stiff ECM, high actomyosin contractility, and low lamin-A favor nuclear rupture d Nuclear rupture causes cytoplasmic mis-localization of DNA repair factors d Repair factor depletion increases DNA damage, telomere loss, and cell-cycle arrest d Lamin-A increases during development to mechano-protect the genome

siRNA and antisense oligonucleotides, AON, have similar size and negative charge and are often packaged for in vitro delivery with cationic lipids or polymers–but exposed positive charge is problematic in vivo. Here we demonstrate loading and functional delivery of RNAi and AON with non-ionic, nano-transforming polymersomes. These degradable carriers are taken up passively by cultured cells after which the vesicles transform into micelles that allow endolysosomal escape and delivery of either siRNA into cytosol for mRNA knockdown or else AON into the nucleus for exon skipping within pre-mRNA. Polymersome-mediated knockdown appears as efficient as common cationic-lipid transfection and about half as effective as Lentivirus after sustained selection. For AON, initial results also show that intramuscular injection into a mouse model of muscular dystrophy leads to the expected protein expression, which occurs along the entire length of muscle. The lack of cationic groups in antisense polymersomes together with initial tests of efficacy suggests broader utility of these non-viral carriers.

Whether cell forces or extracellular matrix (ECM) can impact genome integrity is largely unclear.Here, acute perturbations (~1hr) to actomyosin stress or ECM elasticity cause rapid and reversible changes in lamin-A, DNA damage, and cell cycle. Embryonic hearts, differentiated iPS-cells, and various nonmuscle cell types all show that actomyosin-driven nuclear rupture causes cytoplasmic mis-localization of DNA repair factors and excess DNA damage. Binucleation and micronuclei increase as telomeres shorten, which all favor cell cycle arrest. Deficiencies in lamin-A and repair factors exacerbate these effects, but lamin-A-associated defects are rescued by repair factor overexpression and by contractility modulators in clinical trials. Contractile cells on stiff ECM normally exhibit low phosphorylation and slow degradation of lamin-A by matrix-metalloprotease-2 (MMP2), and inhibition of this lamin-A turnover and also actomyosin contractility is seen to minimize DNA damage. Lamin-A is thus stress-stabilized to mechano-protect the genome.(137 words)

SUMMARY Marrow-derived macrophages are highly phagocytic, but whether they can also traffic into solid tumors and engulf cancer cells is questionable, given the well-known limitations of tumor-associated macrophages (TAMs). Here, SIRPα on macrophages from mouse and human marrow was inhibited to block recognition of its ligand, the “marker of self” CD47 on all other cells. These macrophages were then systemically injected into mice with fluorescent human tumors that had been antibody targeted. Within days, the tumors regressed, and single-cell fluorescence analyses showed that the more the macrophages engulfed, the more they accumulated within regressing tumors. Human-marrow-derived macrophages engorged on the human tumors, while TAMs were minimally phagocytic, even toward CD47-knockdown tumors. Past studies had opsonized tumors in situ with antibody and/or relied on mouse TAMs but had not injected SIRPα-inhibited cells; also, unlike past injections of anti-CD47, blood parameters remained normal and safe. Consistent with tumor-selective engorge-and-accumulate processes in vivo, phagocytosis in vitro inhibited macrophage migration through micropores that mimic features of dense 3D tissue. Accumulation of SIRPα-inhibited macrophages in tumors favored tumor regression for 1–2 weeks, but donor macrophages quickly differentiated toward non-phagocytic, high-SIRPα TAMs. Analyses of macrophages on soft (like marrow) or stiff (like solid tumors) collagenous gels demonstrated a stiffness-driven, retinoic-acid-modulated upregulation of SIRPα and the mechanosensitive nuclear marker lamin-A. Mechanosensitive differentiation was similarly evident in vivo and likely limited the anti-tumor effects, as confirmed by re-initiation of tumor regression by fresh injections of SIRPα-inhibited macrophages. Macrophage motility, phagocytosis, and differentiation in vivo are thus coupled.

The liver is one of the few adult tissues that has the capacity to regenerate following hepatectomy or toxic damage. In examining the early growth response during hepatic regeneration, we found that a highly induced immediate-early gene in regenerating liver encodes RL/IF-1 (regenerating liver inhibitory factor) and is the rat homolog of human MAD-3 and probably of chicken pp4O. RL/IF-1 has IKB activity of broad specificity in that it inhibits the binding of p5O-p65 NF-KB, c-Rel-p50, and RelB-p50, but not p50 homodimeric NF-KB, to KB sites. Like RL/IF-1, several members of the NF-KB and rel family of transcription factors are immediate-early genes in regenerating liver and mitogen-treated cells. We examined changes in KB site binding activity during liver regeneration and discovered a rapidly induced novel KB site-binding complex designated PHF [posthepatectomy factor(s)]. PHF is induced over 1,000-fold within minutes posthepatectomy in a protein synthesisindependent manner, with peak activity at 30 min, and is not induced by sham operation. PHF is distinct from p5O-p65 NF-KB, which is present only in the inactive form in liver posthepatectomy. Although early PHF complexes do not interact strongly with anti-p50 antibodies, PHF complexes present later (3 to 5 h) posthepatectomy react strongly, suggesting that they contain a p50 NF-KB subunit. Unlike p5O-p65 NF-KB, c-Rel-p50, and RelB-p50 complexes, PHF (1, 9, 11, 21, 27-29, 32, 37, 38, 52, 58).We have isolated 41 novel immediate-early genes from regenerating liver and insulin-treated H35 cells and performed extensive analyses of immediate-early gene expression in regenerating liver, insulin-treated H35 cells, and serum-stimulated fibroblasts (37,38). We showed that the majority of immediate-early genes are expressed in all mitogen-treated cells, but about one-third show liver-specific induction. Subsequently, we found that one of the genes that * Corresponding author.we previously identified (37), RL-14, encodes a protein containing notchlike repeats. These repeats have been found in a variety of different proteins ranging from transcription factors to structural proteins (7,8,18,25,30,34,35,40,48,50,54). While we were performing the analysis of RL-14, very similar proteins, MAD-3 and pp4O, were identified and characterized as IKB-like in that they inhibited the binding of the NF-KB transcription factor to DNA (15,20).NF-KB, originally described as a B-cell-specific DNAbinding protein, is a ubiquitous transcription factor composed of p50 and p65 subunits that binds to KB sites found in the regulatory regions of many cellular genes involved in immune responses and/or acute-phase reactions like immunoglobulin K-chain genes, interleukin-2, beta interferon, and others (2,7,18,19,25,31 IKBot and IKB,(3,24,57). In pSO-p65 NF-KB, the binding site for IKB is likely to be on the p65 subunit, as IKB does not inhibit the binding of p50 homodimers to KB sites (4, 39). In cells, p5O-p65 NF-KB is normally present in an inactive, cytoplasmic form complexed with lKB. Activat...