NOTCH4 and plasma cell myeloma: In this regard, both autocrine and paracrine (with osteoblasts) activation of Notch receptor 1 and 2 signaling stimulate the proliferation of myeloma cells.84, 85, 86, 87 Interestingly, osteocytes could use a different set of Notch receptors to communicate with myeloma cells, as bidirectional communication between osteocytes and myeloma cells changed the Notch receptor repertoire in both cell types, with a rapid and marked increase in the expression of Notch receptor 3 and Notch receptor 4.79