During the screening for novel differentiation inducers, we found that a culture broth of Streptomyces sp. HK-803 induced myeloid differentiation of HL-60 cells. The active substance was identified as deamino-hydroxy-phoslactomycin B (HPLM) by mass spectrometry, and synthesized HPLM also induced the differentiation of HL-60 cells. HPLM showed greater inhibition of protein phosphatase 2A (PP2A) activity than phoslactomycin B (PLMB); however, PLMB and okadaic acid did not induce differentiation. Moreover, treatment with ATRA and 1 alpha, 25(OH)(2)D-3 induced retinoic acid receptor-beta and 1 alpha, 25(OH)(2) D-3 24-hydroxylase, respectively, whereas HPLM did not, suggesting that HPLM is a novel differentiation inducer. (C) 2009 Elsevier Inc. All rights reserved.